[Prism] Fix race condition and nil pointer dereferencing

[shunping]

fixes #36366

I ran the tests for about 10k times and saw no failure after the fix.

Prior to that, the failure rate is about 1 in 100 for the race condition and 1 in 1000 for the nil pointer dereferencing.

[gemini-code-assist]

Summary of Changes

Hello @shunping, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the stability and reliability of the prism runner by addressing critical runtime issues. It includes fixes for a potential nil pointer dereference and a race condition, alongside improvements to error handling through more comprehensive logging for panics. These changes collectively aim to prevent unexpected crashes and provide better diagnostic information when issues do occur.

Highlights

• Nil Pointer Dereference Fix: Introduced a nil check for dnt (derived from ss.pendingByKeys[key]) in the buildTriggeredBundle function to prevent potential nil pointer dereferences, ensuring the function returns gracefully if no pending elements are found for a given key.
• Race Condition Mitigation: Implemented a mutex lock (em.refreshCond.L.Lock() and Unlock()) around the scheduling of processing time events (em.processTimeEvents.Schedule) to resolve a potential race condition and ensure thread-safe access to shared resources.
• Enhanced Error Logging: Added structured logging (slog.Error) to capture panics that occur within the ElementManager.Bundles watermark evaluation goroutine, providing more detailed context including the error and traceback for improved debugging.

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[shunping]

R: @liferoad

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.19%. Comparing base (3534960) to head (3f88c27).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...am/runners/prism/internal/engine/elementmanager.go	0.00%	9 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #36370      +/-   ##
============================================
- Coverage     40.20%   40.19%   -0.01%     
  Complexity     3386     3386              
============================================
  Files          1220     1220              
  Lines        186149   186159      +10     
  Branches       3523     3523              
============================================
- Hits          74839    74825      -14     
- Misses       107955   107979      +24     
  Partials       3355     3355              

Flag	Coverage Δ
go	28.42% <0.00%> (-0.03%)	⬇️

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[shunping]

Thanks!