fix(pipeline): stop idle L2 cold-start polling

[YOMXXX]

Summary

• pass the L2 trigger source into runL2 so timer-originated cold-start retries can be distinguished from fresh L1 activity
• stop re-arming maxInterval polling when the cold-start retry still skips and no L2 cursor exists
• keep maxInterval polling unchanged after L2 establishes a cursor, and re-arm normally on the next L1 event
• add regression coverage for the idle skip loop and the established-cursor path

Verification

• npm test
• npm run build

Fixes #155
Related: #193

[Maxwell-Code07]

Awesome work! 13 fixes in one batch covering Gateway hardening, embedding compatibility, Hermes memory injection, offload stability, and pipeline optimization — a very productive cleanup session 👏

We'll review and merge them one by one 🚀