fix(go): close failed session event loops

[green3sf]

Summary

• stop the eagerly started session event consumer when CreateSession fails
• centralize local event-channel shutdown so failure cleanup does not issue a session.destroy RPC
• cover RPC errors, malformed responses, session ID mismatches, and SessionFS initialization failures

Root cause

newSession starts processEvents immediately. The affected error paths removed the pre-registered session from Client.sessions but left its event channel open. Because the failed session was neither returned to the caller nor retained for Client.Stop, its goroutine remained blocked on the channel for the lifetime of the process.

The cleanup now removes only the session instance created by the failing call and closes its event channel without making another RPC.

Impact

Failed non-cloud session creation no longer leaks one goroutine, session object, and buffered event channel per attempt.

Validation

• go test .
• go test -race . -run 'TestClient_CreateSession(Failure|InitializationFailure)ClosesRegisteredSession' -count=1
• git diff --check

Fixes #2320