'alarm_pool_add_repeating_timer_us' Set the repeating time to 500us, and it will not trigger after 5636s.

**RP2040 Board**, After using **alarm_pool_add_repeating_timer_us** to create a 500uS time base for the timer list, After the program runs normally **5636s**, the callback function passed in **alarm_pool_add_repeating_timer_us** will no longer be executed.
Multiple experiments, each time it stopped at **5636s**.
It seems that a parameter in the SDK overflowed.
Looking forward to your suggestions.
Thank you.

Start with the RP2040 implementation and entry point for alarm_pool_add_repeating_timer_us, then reproduce the reported 500us timer case while observing behavior near 5636 seconds. Done means identifying the overflow or timing failure and confirming that the callback continues executing beyond that duration.

Written by the indexing model from the issue text.