feat: Implement Google Cloud SQL IAM database authentication

Introduces a new module `simple_gcp_connector` to facilitate secure connections to Google Cloud SQL databases using IAM authentication.

Key features include:
- `GoogleCloudTokenProvider` for dynamic IAM token generation.
- `CloudSqlInstance` for resolving Cloud SQL instance metadata and IP addresses.
- Integration with `psycopg` (via `GoogleCloudConnInfoProvider`) for connection pooling with IAM.
- Integration with `SQLAlchemy` (via `register_connector`) for dynamic connection arguments and IAM.
- Comprehensive unit and integration tests to ensure functionality.
- Updated `README.md` with detailed usage instructions and examples.
- Initial project setup with `pyproject.toml`, `.gitignore`, and `.python-version`.