…ed readability and maintainability

…iable functionality

- Updated test_mcp_toolset_auth.py to improve code readability and maintainability by restructuring imports and fixtures.
- Added new test cases to validate the behavior of MCPToolset with both authentication and environment callbacks.
- Enhanced mock setups to ensure proper isolation of tests and avoid dependency issues.
- Refactored test assertions for clarity and consistency.
- Updated test_mcp_toolset_env.py to rename environment transform callback for clarity and improved structure.
- Ensured that tests validate the integration of environment variable extraction and injection with the MCPToolset.