Various fixes

[clemsgrs]

Summary

• optimize embedding throughput with batched loading, batch timing instrumentation, async prefetch/copy, and region-aware batch preprocessing
• switch embedding reads to pre-extracted tar-backed tile archives via tiling.save_tiles and TarTileReader, while keeping HS2P coordinate artifacts as the canonical tiling metadata
• rename process-list and artifact references from tiles_* coordinate files to coordinates_*, update docs, and add focused regression coverage for the new tile-store path

Validation

• COVERAGE_FILE=/tmp/slide2vec-region-final.coverage ~/Code/venv/slide2vec/bin/python -m pytest -q tests/test_dependency_split.py tests/test_regression_inference.py tests/test_progress.py -k 'region_batch_preprocessor or region_models or serialize_execution or uses_batched_loader_knobs or batch_timing or run_forward_pass or dependency_split'
• COVERAGE_FILE=/tmp/slide2vec-backend-split.coverage ~/Code/venv/slide2vec/bin/python -m pytest -q tests/test_regression_core.py tests/test_regression_inference.py -k 'execution_options_from_config or execution_options_with_output_dir or serialize_execution or build_hs2p_configs or resolve_embedding_backend or uses_batched_loader_knobs'
• COVERAGE_FILE=/tmp/slide2vec-push.coverage ~/Code/venv/slide2vec/bin/python -m pytest -q tests/test_hs2p_package_cutover.py -k 'load_process_df_requires_hs2p_process_list_columns'
• ~/Code/venv/slide2vec/bin/python -m py_compile slide2vec/api.py slide2vec/data/tile_store.py slide2vec/data/dataset.py slide2vec/inference.py slide2vec/utils/tiling_io.py tests/test_tile_store.py

Notes

• tests/test_tile_store.py was added for the tar-backed reader, but this local venv is missing PIL, so I did not run that file here.
• .claude/settings.local.json remains local and was not included in the branch.