Fix thread-safety issue in LockGuard and ScopedLock by using atomic operations for shared_ptr.

[kevingpqi123]

Fix a race condition in lock acquisition: when one thread was about to lock rootLocker, another thread could call updateRootLocker to replace the shared_ptr, potentially destroying the mutex before the first thread locked it.

Changes:

• LockGuard and ScopedLock now accept a pointer to shared_ptr and use std::atomic_load internally to safely snapshot the shared_ptr before locking.
• updateRootLocker uses std::atomic_store to replace rootLocker atomically.
• PAGPlayer::setSurfaceInternal uses std::atomic_store when updating PAGSurface::rootLocker to keep read/write atomic operations symmetric.
• Added missing #include to LockGuard.h and ScopedLock.h.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 65.32258% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.25%. Comparing base (0dd6334) to head (8509436).

Files with missing lines	Patch %	Lines
src/rendering/PAGPlayer.cpp	38.46%	24 Missing ⚠️
src/rendering/PAGSurface.cpp	36.36%	7 Missing ⚠️
src/rendering/layers/PAGLayer.cpp	80.00%	5 Missing ⚠️
src/rendering/layers/PAGImageLayer.cpp	50.00%	3 Missing ⚠️
src/rendering/layers/PAGTextLayer.cpp	80.00%	2 Missing ⚠️
src/rendering/layers/PAGFile.cpp	85.71%	1 Missing ⚠️
src/rendering/utils/LockGuard.h	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3324      +/-   ##
==========================================
- Coverage   75.25%   75.25%   -0.01%     
==========================================
  Files         503      503              
  Lines       33299    33300       +1     
  Branches    10739    10630     -109     
==========================================
  Hits        25060    25060              
+ Misses       6031     6027       -4     
- Partials     2208     2213       +5     

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[domchen]

改法增加了内存越界访问的风险，要继续分析真正的crash原因，不是这么修改。