roll: pigweed pw_uart: Add UartBase class

Also update the docs to explain the class hierarchy.

Original-Bug: 369678735
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/238092
Original-Revision: 7dc3b1b2a69972ae19bbe43f922aefd6dda73a3e

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: b4e75393442526..7dc3b1b2a69972
Roller-URL: https://ci.chromium.org/b/8735697218738875249
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ibd929f40088757c41f7a85d1d8a72093fcffaf25
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/238275
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/MODULE.bazel b/MODULE.bazel
index ddfd60c..753ef4f 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -49,8 +49,8 @@
     module_name = "pigweed",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-09-26.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8735702464976187665.
-    commit = "b4e75393442526d409968e4aac685515944b3e3e",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8735697218738875249.
+    commit = "7dc3b1b2a69972ae19bbe43f922aefd6dda73a3e",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed",
 )
 
@@ -58,8 +58,8 @@
     module_name = "pw_toolchain",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-09-26.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8735702464976187665.
-    commit = "b4e75393442526d409968e4aac685515944b3e3e",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8735697218738875249.
+    commit = "7dc3b1b2a69972ae19bbe43f922aefd6dda73a3e",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed",
     strip_prefix = "pw_toolchain_bazel",
 )