feat: implement Google Workspace clients foundation

[gcharest]

Summary | Résumé

This pull request introduces a new infrastructure layer for Google Workspace API clients, including a robust, reusable executor for Google API calls with built-in retry and error handling, a session provider for authentication and service instantiation, and a facade for accessing all service clients. It also adds comprehensive unit tests and shared fixtures to ensure reliability and testability.

Google Workspace Infrastructure Layer

• Added a GoogleWorkspaceClients facade class to provide a unified interface for all Google Workspace service clients, improving discoverability and dependency injection. (facade.py)
• Implemented a SessionProvider class to centralize authentication, service account delegation, and Google API service creation, ensuring thread safety and proper credential management. (session_provider.py)
• Created an executor.py module with an execute_google_api_call function that standardizes API call execution, including configurable retries, exponential backoff, rate limit handling, and error normalization. (executor.py)

Testing Infrastructure

• Added a suite of unit tests for the executor module, covering success, retry logic, error handling, and backoff strategies. (test_executor.py)
• Introduced shared test fixtures for mocking Google API services, credentials, and errors, facilitating reliable and isolated unit tests. (conftest.py)
• Added module docstring for test package organization. (__init__.py)

Public API and Documentation

• Provided clear public API documentation and usage examples in the package __init__.py to guide developers in integrating the new infrastructure layer. (__init__.py)