gh-137400: Fix thread-safety issues when profiling all threads

[colesbury]

There were a few thread-safety issues when profiling or tracing all threads via PyEval_SetProfileAllThreads or PyEval_SetTraceAllThreads:

• The loop over thread states could crash if a thread exits concurrently (in both the free threading and default build)
• The modification of c_profilefunc and c_tracefunc wasn't thread-safe on the free threading build.

• Issue: sys._setprofileallthreads race condition #137400