Synchronize native MariaDB abort coverage

[chubes4]

Closes #2444.

Summary

• replace command-count polling with an explicit allocation barrier
• keep the underlying allocation in flight until waiter cancellation is exercised
• settle the exact dependency-keyed readiness operation used by the test

Verification

• npx tsx tests/native-mariadb-runtime-service.test.ts (10 consecutive runs)
• git diff --check

AI assistance

GPT-5.6-sol via OpenCode diagnosed the fast-Linux fixture race, implemented deterministic synchronization, and ran repeated verification under Chris Huber’s direction.