This commit addresses three issues with the gthread worker:
1. Request body handling on keepalive
- Add finish_body() method to Parser to discard unread body bytes
- Call it before returning connections to the poller
- Prevents socket appearing readable due to leftover body
Fixes#3301
2. Timeout reliability with monotonic clock
- Replace time.time() with time.monotonic() in set_timeout()
- Replace time.time() with time.monotonic() in murder_keepalived()
- Prevents timeout issues caused by NTP adjustments
3. SSL error handling
- Move conn.init() from enqueue_req() to handle()
- SSL handshake now runs in worker thread, not main thread
- ENOTCONN errors during ssl_wrap_socket are caught per-connection
- Prevents entire worker crashes on SSL handshake failures
Also adds comprehensive unit tests for the gthread worker.
Closes#3303Closes#3308
