Add workflow race condition simulation tests

[Copilot]

The workflows community_ip_report.yml and false_positive_checker.yml have historically suffered from race conditions (RACE2, RACE5) when parallel runs concurrently write to shared files. No tests existed to verify that the fixes actually hold.

Changes

• tests/test_race_simulations.py — 12 new tests across 4 classes simulating the documented race patterns:

TestRace2AppendOnly

Verifies that append-only writes prevent data loss vs. the old read-modify-write pattern. Includes a deterministic demonstration that RMW silently loses entries on conflict:

# Worker A and B both read the base state, then write back
overwrite_file(logfile, base_content_a + entry_a)  # Worker A
overwrite_file(logfile, base_content_b + entry_b)  # Worker B → entry_a is gone

TestRace5ResetReapplyAppendOnly

Simulates the git diff HEAD → /tmp → reset --hard origin → re-apply loop for append-only log files. Covers single retry, dedup-on-retry (entry already on remote), and 5-attempt retry loops.

TestRace5ResetReapplyOverwrite

Simulates the backup/restore pattern for overwrite-semantics files (false_positive_report.md, false_positives_set.json) across the 5-attempt retry loop.

TestCombinedWorkflowRaceScenario

End-to-end: 2 and 5 parallel workers each operating in isolated directories against a shared in-memory "remote". Verifies no log entry or IP is lost after concurrent push/retry cycles.