refactor: improve integration tests for crash child task runs
- Add proper docstrings explaining why API-level testing is appropriate
- Add test for preserving already-completed tasks
- Add test for crashing pending tasks
- Clean up test structure and imports
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Co-Authored-By: Claude <noreply@anthropic.com>
Fix performance issues with sync tasks on Windows
Removes use of `run_coro_as_sync` in the sync task engine because the
underlying locking is a performance bottleneck on Windows.