Fix timeout handling in SchedulerToExecutorService.awaitTermination

[cuishuang]

This PR fixes timeout handling in SchedulerToExecutorService.awaitTermination().

The previous implementation converted the timeout in the wrong direction:

unit.convert(timeout, TimeUnit.MILLISECONDS)

For example, awaitTermination(1, TimeUnit.SECONDS) converted the value to zero and returned immediately without waiting.

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.592 bits/char
Verdict: ✅ Mid-4 beauty detected (thoughtful human code!)

Changed files entropy:

src/main/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorService.java: 4.431
src/test/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorServiceTest.java: 4.752

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊

[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.62%. Comparing base (947e681) to head (c28196d).

Files with missing lines	Patch %	Lines
...nternal/schedulers/SchedulerToExecutorService.java	84.61%	1 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (84.61%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff            @@
##                4.x    #8301   +/-   ##
=========================================
  Coverage     98.61%   98.62%           
- Complexity     7148     7158   +10     
=========================================
  Files           824      824           
  Lines         50791    50800    +9     
  Branches       6911     6913    +2     
=========================================
+ Hits          50086    50099   +13     
+ Misses          481      476    -5     
- Partials        224      225    +1     

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