test: add comprehensive deadlock prevention suite (28 tests)

Addresses chaos-hacker adversarial review findings:
- HIGH #1: Test _await_idle's actual ghost cleanup branch via time.monotonic patch
- HIGH #2: Test generation_timeout on real step() with ghost IDs + stuck RUNNING
- HIGH #3: Verify snapshot data correctness (not just no-hang) after bump()
- MEDIUM #4: Truly concurrent writes via asyncio.Barrier + serialization proof
- MEDIUM #5: Stuck RUNNING program triggers generation_timeout
- MEDIUM #6: Write serialization assertion (max_concurrent == 1)
- MEDIUM #7: Lock eviction race (concurrent reuse after terminal pop)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: KhrulkovV