This commit introduces type hints for function arguments, return values,
and local variables in `examples/audience_insights/generate_audience_insights.py`.

Key changes include:
- Added type hints to all function signatures and return types.
- Added inline type hints for variables within functions.
- Imported necessary types from `typing`, Google Ads client libraries,
  services, enums, and types modules.
- Ensured proper organization and removal of unused or duplicate imports.
- Updated some variable assignments to use specific Enum members for clarity
  (e.g., `AudienceInsightsDimensionEnum`).
- Replaced some string formatting with f-strings in exception handling.

These changes improve code readability, maintainability, and help with
static analysis, making your example code more robust and easier to understand.

…sights.py` script.

The tests are located in the `examples/audience_insights/test` directory.

Key features of the test suite:
- Mocks the Google Ads API client (v19) and its services (AudienceInsightsService, GoogleAdsService).
- Includes tests for the three main functions:
    - `audience_composition_insights`: Verifies correct API call parameters (customer_id, audience definition, dimensions) and response handling.
    - `generate_suggested_targeting_insights`: Verifies correct API call parameters and response handling.
    - `list_audience_insights_attributes`: Verifies correct API call parameters, dimension usage, and processing of results.
- Includes a test for the `main()` function's logic to ensure it correctly orchestrates calls to the helper functions with appropriate arguments.
- Includes a test for the script's command-line entry point (`if __name__ == "__main__":`) to verify argument parsing and client initialization.
- All tests are designed to use and verify Google Ads API v19 objects and enums.
- The test suite can be run using standard Python unittest mechanisms.

Add test suite for examples/audience_insights

This commit introduces a new test suite for the Google Ads API Python examples related to audience insights, specifically for `generate_audience_insights.py`.

The test suite is located in `examples/audience_insights/tests/` and uses the `unittest` framework.

Key features of the test suite:
- Mocks the GoogleAdsClient and its services (AudienceInsightsService, GoogleAdsService) to prevent actual API calls.
- Verifies correct request construction for:
    - `audience_composition_insights`
    - `generate_suggested_targeting_insights`
    - `list_audience_insights_attributes`
- Tests the `main` function for both successful execution paths and exception handling (specifically `GoogleAdsException`).
- Ensures that client enum values and service paths are correctly used.
- Includes checks for console output where appropriate (e.g., for `list_audience_insights_attributes`).

The tests ensure that the example script's logic is sound and that it interacts with the (mocked) client library as expected for Google Ads API v19.