Add Afar1 species support for Anopheles farauti in the Pacific

[iftiquar]

Summary

• Implements the Afar1 API client class for accessing Anopheles farauti genomic data from Google Cloud Storage, following the established pattern of existing species (Adir1, Amin1, Af1). This enables open-source genomic surveillance tools for a key malaria vector responsible for transmission in the Pacific region (Papua New Guinea, Solomon Islands, Vanuatu).
• Adds complete test infrastructure including Afar1Simulator with simulated genome/GFF/SNP/metadata generation, fixture metadata CSVs for Pacific region samples, and case_afar1 test parametrization across 6 unit test modules (base, snp_data, snp_frq, sample_metadata, heterozygosity, g123).
• Adds Sphinx API documentation (Afar1.rst) and updates the docs landing page with an Afar1 grid card.
• Fixes a pre-existing bug in Adar1.__repr__/_repr_html_ where documentation URLs incorrectly pointed to Adir1.html instead of Adar1.html.

Changes

New files

• malariagen_data/afar1.py — Afar1 class with GCS configuration, taxon colors, cache names, __repr__/_repr_html_
• docs/source/Afar1.rst — Sphinx API documentation listing all available analysis functions
• tests/integration/test_afar1.py — Skeleton integration test with setup_afar1 helper
• tests/anoph/fixture/vo_afar_release_master_us_central1/ — Fixture metadata CSVs (30 samples across PNG, SLB, VUT)

Modified files

• malariagen_data/__init__.py — Register Afar1 export
• malariagen_data/adar1.py — Fix doc URL bug (Adir1.html → Adar1.html)
• docs/source/index.rst — Add Afar1 grid card to landing page
• tests/anoph/conftest.py — Add Afar1Simulator class and afar1_sim_fixture
• tests/anoph/test_{base,snp_data,snp_frq,sample_metadata,heterozygosity,g123}.py — Add afar1_sim_api fixtures and case_afar1_sim parametrization

Test plan

• Verify unit tests pass with pytest tests/anoph/ -x (includes Afar1 parametrized cases)
• Verify from malariagen_data import Afar1 works correctly
• Verify Afar1.__repr__() and Afar1._repr_html_() produce correct output
• Verify Sphinx docs build without errors: cd docs && make html
• Integration test pytest tests/integration/test_afar1.py (requires GCS access)