fix(ssh-for-commander): fix clissh goroutine leaks

[faroyam]

clissh

pkg/ssh/clissh/process/executor.go

• Added storage for read-side pipe file descriptors.
• Close write, read, and handler pipe ends on Stop, timeout, and normal exit.
• Made Stop idempotent using sync.Once and atomics.
• The timeout goroutine now terminates after the process exits.
• readFromStreams exits on os.ErrClosed instead of looping.

pkg/ssh/clissh/tunnel.go

• Added storage for stdout and stdin pipe file descriptors.
• Tunnel.Stop() now closes pipes and kills the process even when HealthMonitor was not started.
• HealthMonitor exits when the tunnel has already been stopped.
• The wait goroutine closes the pipe set for its own run without affecting the next run.

gossh

pkg/ssh/gossh/client.go

• Added synchronized lifecycle state for Start, Stop, and keepalive restart.
• Stop() now marks the client as stopped before cleanup, so new sessions fail fast after stop.
• Repeated Start() now closes the previous SSH client, sessions, keepalive goroutine, connections, local kube-proxies, and SSH agent socket connection before reconnecting.
• Keepalive now has its own stopCh and doneCh; stopKeepAlive() waits for shutdown with a timeout instead of blocking forever.
• Keepalive restart() no longer resurrects a stopped client and ignores stale restarts from an old keepalive run.
• SSH sessions and SSH client access now use snapshots under mutexes to avoid races.
• Local kubeProxies access is synchronized and reset during reconnect/stop.
• Remote kube-proxy cleanup commands can still create SSH sessions during stop via an internal allowStopped path.

pkg/ssh/gossh/keepalive.go

• Keepalive checks now use thread-safe SSH client/session snapshots.
• Sleep between retries is interruptible through stopCh.
• Session keepalive iteration no longer reads sshSessionsList directly.

pkg/ssh/gossh/command.go

• Added internal newSSHCommand(..., allowStopped) helper.
• Public commands still reject stopped clients, while stop-cleanup commands can run during client shutdown.

pkg/ssh/gossh/tunnel.go

• Tunnel now gets the SSH client through a safe snapshot.
• Concurrent Stop() no longer causes a nil pointer panic while dialing a remote tunnel endpoint.

pkg/ssh/gossh/reverse-tunnel.go

• ReverseTunnel now gets the SSH client through a safe snapshot.
• Concurrent Stop() now returns a normal error instead of panicking on GetClient().Listen(...).

pkg/ssh/base/kubeproxy/kube_proxy.go

• Made the proxy port readiness timeout test-configurable.
• Stop the proxy command when port readiness times out.
• Stop the proxy command when the port-ready signal arrives with an empty port.