Bug report

The _PySemaphore_PlatformWait function in parking_lot.c has three implementations:

• WaitForSingleObjectEx (for Windows)
• sem_timedwait (Linux and most other POSIX platforms)
• pthread_cond_timedwait (macOS and possibly other platforms that don't have sem_timedwait)

We should follow the pattern used in thread_pthread.h where we prefer functions that support CLOCK_MONOTONIC. These are sem_clockwait and pthread_cond_timedwait after setting pthread_condattr_setclock.

Additionally, we should use _PyTime_AsTimespec_clamp instead of _PyTime_AsTimespec (we don't want to raise errors in these code paths).

Note that:

1. Windows doesn't need any changes because WaitForSingleObjectEx isn't relative to any specific clock -- it just takes a timeout for N milliseconds in the future
2. macOS doesn't support pthread_condattr_setclock, so we're stuck with the system clock on macOS. It's not clear to me if we use the pthread_cond_timedwait for any other OS.

Linked PRs

• gh-112606: Use monotonic clock when supported in semaphore waiting in parking_lot.c #112614
• gh-112606: Use pthread_cond_timedwait_relative_np in parking_lot.c when available #112616
• gh-112606: Use sem_clockwait with monotonic time when supported in parking_lot.c #112733