bugfix(threading): Ensure thread list critical section remains valid during CRT shutdown

[seer-by-sentry]

Fixes CLIENT-38C. The issue was that: Thread unregistration attempts to acquire a critical section lock whose underlying Windows handle is invalidated during application shutdown, causing an access violation.

• Replaced the CriticalSectionClass used for ThreadList synchronization with a raw Windows CRITICAL_SECTION.
• Allocated the CRITICAL_SECTION from the Windows process heap (GetProcessHeap) to guarantee its validity throughout the application's lifetime, even during CRT heap teardown.
• Implemented thread-safe, one-time initialization for the critical section using InterlockedCompareExchangePointer.
• Introduced ScopedThreadListLock as an RAII guard for the new raw CRITICAL_SECTION.
• Updated thread registration/unregistration and main thread ID retrieval to use the new synchronization mechanism.

This fix was generated by Seer in Sentry, triggered by x64-dev. 👁️ Run ID: 13508812

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