feat(rollout): add filtered reads

[xuzha]

Summary

• add typed exact-match rollout filters for rollout, problem, policy, role, training eligibility, and artifact type
• push filters into Lance LsmScanner sources before merge/deduplication, with pagination applied after deduplication
• expose filtered reads across embedded Rust, REST, remote clients, PyO3, and sync/async Python APIs
• document reproducible policy-version reads for RolloutDB learners

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --offline -- -D warnings
• cargo test --workspace --offline
• python/.venv/bin/pytest -q python/tests/test_rollout.py (8 passed)
• python/.venv/bin/pytest -q python/tests/test_rollout_remote.py (3 passed)
• uv run --frozen ruff format --check python/
• uv run --frozen ruff check python/
• uv run --frozen --extra dev pyright

Testing notes

• The repository CI helper currently references the removed rust/lance-context/Cargo.toml; the corrected root-workspace commands above were run directly.
• The broad local Python suite reports 184 passed, 10 failed, 2 skipped, and 1 xfailed. The 10 failures reproduce on current main: eight stale DummyInner signatures in test_search.py and two macOS moto/S3 failures.

[beinan]

@copilot resolve the merge conflicts in this pull request