Port interactive TTY test to Go and remove Python integration tests (#2634)
* Port interactive TTY test to Go
- Add TestInteractiveTTY and TestInteractiveTTYEchoCommand in
integration-tests/pty/ package using github.com/creack/pty
- Tests verify cog run works with interactive PTY sessions
- Remove Python test_run_shell_with_with_interactive_tty
- Update README to reflect PTY tests are now implemented
* Remove Python integration tests - all ported to Go
- Remove test-integration/ directory entirely
- Remove tox integration environment
- Update Makefile to consolidate test-integration-go into test-integration
- Update CI workflow to remove Python integration test jobs
- Update CONTRIBUTING.md, AGENTS.md, and README documentation
- Update pyproject.toml to remove test-integration lint exclusions
All integration tests now live in integration-tests/ using Go testscript.
* Add CODEOWNERS to auto-request review from @replicate/cog
---------
Co-authored-by: Mark Phelps <mphelps@cloudflare.com>