pw_spin_delay: Have Micros() return 64-bit value.

A 32-bit value is only 71 minutes, so users would need to add
logic to detect a value wrap. 64-bit values wrap every 500K years.

All implementations already call into API functions which
return 64-bit values, or they use a 32-bit millisecond
api/counter and can cast before multiplying by 1000.

| Platform   | API                   | Value Type        |
| ---------- | --------------------- | ----------------- |
| Arduino    | micros()              | unsigned long     |
| Host       | std::chrono::duration | long long         |
| MCUxpresso | msec counter          | uint32_t          |
| rp2040     | to_us_since_boot()    | uint64_t          |
| stm32cube  | HAL_GetTick()         | uint32_t in msec. |

Note: This function is currently unused.
Change-Id: I1cc67de17b7e3e7b2a21f6024079e1edf5b3ed05
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126110
Reviewed-by: Anthony DiGirolamo <tonymd@google.com>
Commit-Queue: Chris Mumford <cmumford@google.com>
diff --git a/pw_spin_delay_mcuxpresso/delay.cc b/pw_spin_delay_mcuxpresso/delay.cc
index de78ee6..f1a579a 100644
--- a/pw_spin_delay_mcuxpresso/delay.cc
+++ b/pw_spin_delay_mcuxpresso/delay.cc
@@ -29,11 +29,7 @@
 bool s_initialized = false;
 volatile uint32_t s_msec_count = 0;
 
-void UTickCallback(void) {
-  // clang-format off
-  s_msec_count++;
-  // clang-format on
-}
+void UTickCallback(void) { s_msec_count++; }
 
 void InitTickTimer() {
   s_initialized = true;
@@ -54,11 +50,11 @@
   return s_msec_count;
 }
 
-uint32_t Micros() {
+uint64_t Micros() {
   if (!s_initialized) {
     InitTickTimer();
   }
-  return s_msec_count * 1000;
+  return static_cast<uint64_t>(s_msec_count) * 1000;
 }
 
 }  // namespace pw::spin_delay