Enable pytest plugin integration and verify all core features

- Add pytest11 entry point for automatic plugin discovery
- Verify pytest integration works with use_mocktopus fixture
- Confirm Anthropic Messages API (/v1/messages) works correctly
- Validate Record/Replay functionality with .jsonl format
- All promised README features now fully functional

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: haasonsaas

pyproject.toml

@@ -23,6 +23,9 @@ Homepage = "https://github.com/evalops/mocktopus"
 [project.scripts]
 mocktopus = "mocktopus.cli:main"
 
+[project.entry-points.pytest11]
+mocktopus = "mocktopus.pytest_plugin"
+
 [tool.hatch.build.targets.wheel]
 packages = ["src/mocktopus"]