Address integration test review feedback
- Restore random_string/remove_docker_image helpers for pytest fixtures
- Keep remaining Python tests typed and passing
- Strengthen Go tests:
* build_cog_version_match now compares package vs CLI versions (with dev fallback)
* build_base_image_sha ensures label matches actual RootFS layer
* Added predict_json_stdin_dash to cover '--json -'
Re-ran targeted Go integration tests (build_cog_version_match, build_base_image_sha, predict_json_stdin_dash).