chore: prepare 0.1.2 release

[loookashow]

Summary

Prepare 0.1.2 with the latest diarization quality improvements and updated benchmark documentation.

Changes

• Improve automatic speaker-count selection with silhouette refinement plus a small larger-k prior.
• Keep the previous temporal speaker-label smoothing improvements documented in the pipeline docs.
• Add scripts/benchmark_rttm.py for reproducible audio+RTTM benchmark runs across VoxConverse, AMI, and similar datasets.
• Update package version metadata to 0.1.2 and sync runtime diarize.__version__.
• Update README/docs with current VoxConverse numbers and preliminary AMI validation.
• Document known limitations around speaker-count errors and speaker label fragmentation.

Validation

• python -m ruff check .
• python -m ruff format --check .
• python -m pytest tests/test_diarize.py -q
• python -m mkdocs build --strict --site-dir /private/tmp/diarize-site

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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