Upgrade minimum eventlet version to 0.40.3 to address security
vulnerabilities:
- CVE-2021-21419 (Moderate 6.9): Websocket memory exhaustion via
large/compressed frames (fixed in 0.31.0)
- CVE-2025-58068 (Moderate 6.3): HTTP Request Smuggling via improper
trailer handling (fixed in 0.40.3)
Also restructure module to call monkey_patch() at import time for
better patching coverage, while keeping hubs.use_hub() in the worker's
patch() method since it creates OS resources that don't survive fork.
Add comprehensive tests for the eventlet worker.