Fix unused return value warnings in upb call sites and tests.

Several functions in upb marked with UPB_NODISCARD had their return values ignored in test and wrapper call sites.

Check and assert the return values of upb_Message_SetString, upb_Message_SetInt32, upb_ExtensionRegistry_AddArray, _upb_Message_AddUnknown, upb_Array_New, and _upb_Array_ResizeUninitialized across upb and protobuf tests and wrappers.

PiperOrigin-RevId: 967461770
diff --git a/upb/message/internal/compare_unknown_test.cc b/upb/message/internal/compare_unknown_test.cc
index 7346111..a8deb3b 100644
--- a/upb/message/internal/compare_unknown_test.cc
+++ b/upb/message/internal/compare_unknown_test.cc
@@ -286,8 +286,8 @@
   // 4. Create msg2 with raw unknown bytes representing A
   upb_test_ModelWithExtensions* msg2 =
       upb_test_ModelWithExtensions_new(arena.ptr());
-  UPB_PRIVATE(_upb_Message_AddUnknown)(UPB_UPCAST(msg2), buf, size, arena.ptr(),
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)(
+      UPB_UPCAST(msg2), buf, size, arena.ptr(), kUpb_AddUnknown_Copy));
 
   // 5. Verify they compare equal under IncludeUnknownFields
   bool is_equal = upb_Message_IsEqual(UPB_UPCAST(msg1), UPB_UPCAST(msg2),
@@ -326,8 +326,8 @@
 
   // 4. Create msg2 with raw unknown bytes representing A
   upb_test_TestMessageSet* msg2 = upb_test_TestMessageSet_new(arena.ptr());
-  UPB_PRIVATE(_upb_Message_AddUnknown)(UPB_UPCAST(msg2), buf, size, arena.ptr(),
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)(
+      UPB_UPCAST(msg2), buf, size, arena.ptr(), kUpb_AddUnknown_Copy));
 
   // 5. Verify they compare equal under IncludeUnknownFields
   bool is_equal = upb_Message_IsEqual(UPB_UPCAST(msg1), UPB_UPCAST(msg2),
diff --git a/upb/message/promote_test.cc b/upb/message/promote_test.cc
index 85c10fc..f10d6d0 100644
--- a/upb/message/promote_test.cc
+++ b/upb/message/promote_test.cc
@@ -535,7 +535,8 @@
   val_str.str_val = upb_StringView_FromString("World");
   const upb_MiniTableField* custom_f =
       upb_MiniTable_GetFieldByIndex(custom_sub_table, 0);
-  upb_Message_SetString(extension1, custom_f, val_str.str_val, arena.ptr());
+  EXPECT_TRUE(upb_Message_SetString(extension1, custom_f, val_str.str_val,
+                                    arena.ptr()));
 
   // 4. Attach custom parsed submessage "World" to msg as a non-canonical
   // extension under the different custom mini-table layout.
@@ -660,7 +661,7 @@
   upb_Message* extension1 = _upb_Message_New(custom_sub_table_ext, arena.ptr());
   const upb_MiniTableField* custom_f =
       upb_MiniTable_GetFieldByIndex(custom_sub_table_ext, 0);
-  upb_Message_SetInt32(extension1, custom_f, 42, arena.ptr());
+  EXPECT_TRUE(upb_Message_SetInt32(extension1, custom_f, 42, arena.ptr()));
 
   // 7. Attach it as a non-canonical extension to msg using field 1547
   UPB_PRIVATE(_upb_Message_SetNonCanonicalExtension)(
diff --git a/upb/message/test.cc b/upb/message/test.cc
index 036944e..d951159 100644
--- a/upb/message/test.cc
+++ b/upb/message/test.cc
@@ -968,9 +968,9 @@
 
   // Add some standard raw unknown bytes
   char raw_unknown[] = "\x08\x96\x01";  // tag 1 = 150
-  UPB_PRIVATE(_upb_Message_AddUnknown)(UPB_UPCAST(msg), raw_unknown,
-                                       sizeof(raw_unknown) - 1, arena.ptr(),
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)(
+      UPB_UPCAST(msg), raw_unknown, sizeof(raw_unknown) - 1, arena.ptr(),
+      kUpb_AddUnknown_Copy));
 
   // Verify both are present initially
   {
diff --git a/upb/wire/encode_test.cc b/upb/wire/encode_test.cc
index abc67cc..9dfc294 100644
--- a/upb/wire/encode_test.cc
+++ b/upb/wire/encode_test.cc
@@ -233,7 +233,8 @@
   // Verify that the encoded bytes can be decoded back using the registry!
   upb_ExtensionRegistry* ext_reg = upb_ExtensionRegistry_New(arena);
   const upb_MiniTableExtension* ext_array[1] = {upb_wire_test_ext_i32_ext};
-  upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 1);
+  EXPECT_EQ(upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 1),
+            kUpb_ExtensionRegistryStatus_Ok);
 
   upb_wire_test_TestExtensions* decoded_msg =
       upb_wire_test_TestExtensions_parse_ex(buf, size, ext_reg, 0, arena);
@@ -261,9 +262,9 @@
 
   // 3. Also add some standard raw unknown bytes (tag 150)
   char raw_unknown[] = "\x08\x96\x01";  // tag 1 = 150
-  UPB_PRIVATE(_upb_Message_AddUnknown)((upb_Message*)msg, raw_unknown,
-                                       sizeof(raw_unknown) - 1, arena,
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)(
+      (upb_Message*)msg, raw_unknown, sizeof(raw_unknown) - 1, arena,
+      kUpb_AddUnknown_Copy));
 
   // Encode the message WITH kUpb_EncodeOption_SkipUnknown option!
   char* buf;
@@ -280,7 +281,8 @@
   upb_ExtensionRegistry* ext_reg = upb_ExtensionRegistry_New(arena);
   const upb_MiniTableExtension* ext_array[2] = {
       upb_wire_test_ext_i32_ext, upb_wire_test_ext_recursive_ext};
-  upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 2);
+  EXPECT_EQ(upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 2),
+            kUpb_ExtensionRegistryStatus_Ok);
 
   upb_wire_test_TestExtensions* decoded_msg =
       upb_wire_test_TestExtensions_parse_ex(buf, size, ext_reg, 0, arena);
@@ -331,7 +333,8 @@
   upb_ExtensionRegistry* ext_reg = upb_ExtensionRegistry_New(arena);
   const upb_MiniTableExtension* ext_array[2] = {
       upb_wire_test_ext_i32_ext, upb_wire_test_ext_recursive_ext};
-  upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 2);
+  EXPECT_EQ(upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 2),
+            kUpb_ExtensionRegistryStatus_Ok);
 
   upb_wire_test_TestExtensions* decoded_msg =
       upb_wire_test_TestExtensions_parse_ex(buf, size, ext_reg, 0, arena);
@@ -387,9 +390,9 @@
 
   // 3. Also add some standard raw unknown bytes (tag 150)
   char raw_unknown[] = "\x08\x96\x01";  // tag 1 = 150
-  UPB_PRIVATE(_upb_Message_AddUnknown)((upb_Message*)msg, raw_unknown,
-                                       sizeof(raw_unknown) - 1, arena,
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)(
+      (upb_Message*)msg, raw_unknown, sizeof(raw_unknown) - 1, arena,
+      kUpb_AddUnknown_Copy));
 
   // Encode the message WITH kUpb_EncodeOption_SkipUnknown |
   // kUpb_EncodeOption_Deterministic!
@@ -408,7 +411,8 @@
   upb_ExtensionRegistry* ext_reg = upb_ExtensionRegistry_New(arena);
   const upb_MiniTableExtension* ext_array[2] = {
       upb_wire_test_ext_i32_ext, upb_wire_test_ext_recursive_ext};
-  upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 2);
+  EXPECT_EQ(upb_ExtensionRegistry_AddArray(ext_reg, ext_array, 2),
+            kUpb_ExtensionRegistryStatus_Ok);
 
   upb_wire_test_TestExtensions* decoded_msg =
       upb_wire_test_TestExtensions_parse_ex(buf, size, ext_reg, 0, arena);
@@ -437,9 +441,9 @@
 
   // 1. Add Unknown 1 (Tag 10, Varint)
   char unknown1[] = "\x50\x64";
-  UPB_PRIVATE(_upb_Message_AddUnknown)((upb_Message*)msg, unknown1,
-                                       sizeof(unknown1) - 1, arena,
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)((upb_Message*)msg, unknown1,
+                                                   sizeof(unknown1) - 1, arena,
+                                                   kUpb_AddUnknown_Copy));
 
   // 2. Add Non-Canonical Extension 1 (Tag 100, ext_i32)
   int32_t val1 = 42;
@@ -448,9 +452,9 @@
 
   // 3. Add Unknown 2 (Tag 12, Varint)
   char unknown2[] = "\x60\x64";
-  UPB_PRIVATE(_upb_Message_AddUnknown)((upb_Message*)msg, unknown2,
-                                       sizeof(unknown2) - 1, arena,
-                                       kUpb_AddUnknown_Copy);
+  EXPECT_TRUE(UPB_PRIVATE(_upb_Message_AddUnknown)((upb_Message*)msg, unknown2,
+                                                   sizeof(unknown2) - 1, arena,
+                                                   kUpb_AddUnknown_Copy));
 
   // 4. Add Canonical Extension 1 (Tag 101, ext_recursive)
   upb_wire_test_TestRecursive* sub_msg = upb_wire_test_TestRecursive_new(arena);