…them to API v19.

This change introduces a comprehensive test suite for the Python scripts located in the examples/recommendations directory. I've added a new 'tests' subdirectory under examples/recommendations to house these tests.

Key changes include:
- Creation of test files for:
    - detect_and_apply_recommendations.py
    - dismiss_recommendation.py
    - generate_budget_recommendations.py
    - get_recommendation_impact_metrics.py
- Each test file uses the unittest framework with unittest.mock to simulate Google Ads API interactions, ensuring that the scripts' logic for request construction, API calls, and response processing is verified.
- I've updated generate_budget_recommendations.py and get_recommendation_impact_metrics.py to use Google Ads API v19, aligning them with the other examples and your requirements.
- I've run all tests and confirmed they pass.

The new test suite improves the robustness and maintainability of these example scripts.