feat(python): expose BlobFile.read_ranges

[keunhong]

lance.BlobFile gained a positioned read_range(offset, length) (cursor-untouched, GIL-released). Consumers that sample sparse ranges from large blobs — e.g. ML dataloaders fetching 64 spread video frames out of a 1024-frame blob — currently must build caller-side thread pools over read_range to avoid serial object-store round trips. The Rust BlobFile already has the right primitive: read_ranges(&[Range<u64>]), which returns results in input order and lets the ScanScheduler reorder/coalesce/split the physical requests. Only the Python binding is missing. This change exposes it: one vectored call replaces N caller-side threads and gives the scheduler the whole access pattern at once.

Changes

• pyo3 binding (python/src/dataset/blob.rs): new LanceBlobFile.read_ranges mirroring the read_range pattern — (offset, length) pairs converted to Range<u64> with per-range overflow checks, GIL released across the await via the background executor, PyBytes built after the call returns.
• Python wrapper (python/python/lance/blob.py): BlobFile.read_ranges(ranges: list[tuple[int, int]]) -> list[bytes] — results in input order; out-of-bounds ranges raise ValueError, matching read_range.
• Type stubs (__init__.pyi): added read_ranges and the previously missing read_range entry on LanceBlobFile.
• Tests (python/python/tests/test_blob.py): parity with sequential read_range (empty / empty-ranges / non-monotonic / duplicated+overlapping, parametrized), literal input-order preservation, cursor invariance (including after seek), and out-of-bounds/overflow pinned to ValueError with the same messages the dataset-level read_blob_ranges tests pin.

Purely additive — no Rust-core changes, no new dependencies, no async Python API.

Verification

• Full python/tests/test_blob.py passes (177 tests).
• Verified: results identical to sequential read_range on 50 randomized range sets (up to 68 shuffled, duplicated, overlapping ranges over a 4 KB blob), cursor invariant throughout.
• uv run make format idempotent; uv run make lint (ruff + pyright + rustfmt + clippy -D warnings) clean; all pre-commit hooks pass.

[lance-gatekeeper]

✅ Gate recommendation: approve.

This exposes the existing Rust multi-range primitive at the right boundary, preserving blob-local bounds, input order, cursor state, and GIL-released I/O while avoiding caller-managed scheduling.

[lance-gatekeeper]

✅ Gate recommendation: approve.

This exposes the existing Rust multi-range primitive at the right boundary, preserving blob-local bounds, input order, cursor state, and GIL-released I/O while avoiding caller-managed scheduling.