feat(firestore): drop Python 3.7-3.9 support and regenerate

[chalmerlowe]

This PR updates python to establish version 3.10 as the minimum supported version.

Changes

• Configuration & Dependencies:

  • Updated the Python support matrix and classifiers across setup.py, noxfile.py, and CONTRIBUTING.rst to require Python >= 3.10.
  • Regenerated and synchronized EOL runtime constraints files.
  • Cleaned up and pruned obsolete warning filters inside pytest.ini that were previously used for Python < 3.10.

• Test Suite Enhancements:

  • Refactored test_pipeline_explain_options_explain_mode inside both test_system.py and test_system_async.py.
  • Previously, the tests expected an InvalidArgument exception since Explain mode wasn't supported on pipeline queries. Since the live backend now natively supports Explain mode on Pipeline queries, the tests were updated to assert successful plan metrics execution and verify that the correct ExplainStats protobuf structures are returned.

• Librarian Generator Post-Processing:

  • Configured and integrated permanent EOL post-processing rules directly inside .librarian/generator-input/client-post-processing/firestore-integration.yaml to ensure that all future gapic-generator runs automatically preserve these EOL constraints changes and avoid generator overwrites.

[gemini-code-assist]

Code Review

This pull request drops support for Python 3.7, 3.8, and 3.9 across the google-cloud-firestore package, updating the minimum supported version to Python 3.10. The changes include updates to the documentation, pytest configurations, and testing constraints. The review feedback points out that when updating Python versions in documentation examples (such as nox commands in CONTRIBUTING.rst), the current stable release version (e.g., 3.12) should be used instead of the minimum supported version (3.10) or a pre-release version (3.14) to ensure examples remain relevant and functional for most developers.

[daniel-sanche]

LGTM