fix: use native Windows process liveness checks

[Pimpmuckl]

Summary

• replace per-poll tasklist.exe process checks with kernel32 OpenProcess and WaitForSingleObject
• preserve deliberate live, exited, missing, invalid, and access-denied behavior
• close every acquired Windows handle and leave the non-Windows path unchanged

Validation

• uv run pytest plugins/review-suite/tests/test_review_suite_local.py -q: 89 passed
• uv run pytest plugins/review-suite/tests -q: 644 passed
• uv run ruff check on the changed script and test file: passed
• Review Suite fast rvw_8fd40a6a: two reviewers clean