fix: gofmt Go generated files and fix Python test for fork PRs

- Run gofmt on go/rpc/generated_rpc.go and go/generated_session_events.go
  to fix spaces→tabs formatting that caused the Codegen Check to fail.
- Fix test_resume_session_forwards_client_name to return a mock response
  for session.resume instead of forwarding to the real CLI, which requires
  the COPILOT_HMAC_KEY secret unavailable to fork PRs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: patniko