Starrocks db connection close

[Nitin Bhakar (nitinbhakar)]

Summary

• Closing the gRPC client was not enough: StarRocks keeps the FE Flight SQL session in its token cache (visible in SHOW PROCESSLIST) until CloseSession is sent with the handshake bearer token, or until wait_timeout (default 8h).
• closeFlightClient now sends CloseSession with that token, then closes the gRPC connection. Same path for job cleanup and health checks.
• Also closes the client if authentication fails, so a half-open socket is not left behind.

Test plan

• Run a StarRocks query through Heimdall and confirm the FE session disappears from SHOW PROCESSLIST immediately after the job finishes (not after 8h).
• Confirm health checks do not leave sessions behind.
• Confirm a failed auth attempt does not leak a gRPC connection.
• Confirm a cancelled/timed-out job still closes the session (cleanup uses a 5s independent timeout, not the job context).