[Python] Fix race condition in requirements cache creation

[NayanMathur411]

Fixes #36847

This fixes race condition occured in requirements cache creation when starting multiple pipelines together.

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Summary of Changes

Hello @NayanMathur411, 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 addresses a critical race condition within the Apache Beam Python SDK that previously arose when multiple pipelines attempted to create the same requirements cache directory concurrently. The core change involves making the directory creation operation robust against simultaneous calls, thereby preventing potential errors and ensuring smooth operation in parallel environments. A comprehensive new test has been added to validate the fix under simulated concurrent conditions.

Highlights

• Race Condition Fix: Resolved a race condition that occurred during the creation of the requirements cache when multiple pipelines were started simultaneously, by ensuring the directory creation is idempotent.
• Idempotent Directory Creation: The os.makedirs call for the requirements cache path now includes exist_ok=True, preventing errors if the directory already exists due to concurrent operations.
• Concurrency Test Added: A new test case, test_requirements_cache_creation_no_race_condition, has been introduced to simulate concurrent cache directory creation and verify that the fix correctly handles these scenarios without failure.

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[NayanMathur411]

R: @hjtran

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I'm going to defer to someone else here.

[hjtran]

assign set of reviewers

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R: @tvalentyn for label python.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.04%. Comparing base (c6fc698) to head (ce12752).
⚠️ Report is 32 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #37042       +/-   ##
=============================================
+ Coverage     40.37%   57.04%   +16.67%     
  Complexity     3476     3476               
=============================================
  Files          1226     1226               
  Lines        188407   188602      +195     
  Branches       3607     3607               
=============================================
+ Hits          76063   107593    +31530     
+ Misses       108946    77610    -31336     
- Partials       3398     3399        +1     

Flag	Coverage Δ
python	80.76% <100.00%> (+40.13%)	⬆️

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