SSH: Fix/Refactor SSH request creation timing

[dcoric]

Current SSH server implementation creates the request object and executes the security chain before pack data is available from the stream. This needs refactoring to ensure proper ordering.

[dcoric]

In src/proxy/ssh/server.ts, handlePushOperation now buffers the entire pack (packDataChunks), waits for the stream to end, and only then forges the synthetic request and calls chain.executeChain. The forwarding to the upstream host doesn’t kick in until that security chain completes successfully. The SSH integration test suite exercises this sequencing (including the oversized-pack rejection path), and the full mocha/nyc runs finish cleanly.
So the ticket can be marked as done.