fix: resolve flaky tests across platforms and Python versions, appearing on main branch

[bhimrazy]

What does this PR do?

Fixes flaky test failures that were occurring inconsistently across different platforms and Python versions in CI. Currently can be seen in main branch.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84%. Comparing base (21f7686) to head (3cf941b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #649   +/-   ##
===================================
- Coverage    85%    84%   -1%     
===================================
  Files        39     39           
  Lines      3212   3212           
===================================
- Hits       2721   2702   -19     
- Misses      491    510   +19     

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[Copilot]

Pull request overview

This PR addresses flaky test failures occurring inconsistently across different platforms and Python versions in the CI pipeline. The changes focus on improving test reliability through better async event loop handling, platform-specific timing adjustments, and CI workflow optimization.

• Migrates from asyncio.get_event_loop().run_until_complete() to asyncio.run() for better cross-platform event loop handling
• Adds platform-specific timeout adjustments for macOS to account for slower process spawning
• Increases batch timeout values to accommodate varying platform performance
• Optimizes CI workflow to only cancel in-progress runs for pull requests

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/unit/test_loops.py	Replaces deprecated event loop pattern with asyncio.run() for async method calls in synchronous test functions
tests/unit/test_lit_server.py	Increases worker restart wait time from 2 to 5 seconds on macOS with explanatory comment
tests/unit/test_batch.py	Increases batch timeout test parameter from 0.1 to 0.5 seconds for improved stability
.github/workflows/ci-testing.yml	Makes cancel-in-progress conditional, only applying to pull request events

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