[ABA-30] fix(vortex-sparse): normalize patches dtype before slot construction

[abnobdoss]

Summary

Sparse::try_new_from_patches called SparseData::make_slots(&patches) on the caller's Patches before SparseData::from_patches ran normalize_patches_dtype. When fill_value.dtype() differed from patches.values().dtype() in nullability, the slot ArrayRef captured the un-normalized values while the array's declared dtype and SparseData reflected the normalized fill dtype. The constructor commits the inconsistent parts via Array::from_parts_unchecked, so the mismatch was committed silently — and any consumer that reads patches via SparseExt::patches (which rebuilds Patches from the slots) saw the wrong nullability.

Fix: reorder so normalize_patches_dtype runs before make_slots, then call from_patches_unchecked since normalization has already happened. The sibling constructors (Sparse::try_new and SparseData::from_patches) are unchanged.

Two-commit layout: the first commit adds a failing regression test; the second applies the reorder.

 pub fn try_new_from_patches(patches: Patches, fill_value: Scalar) -> VortexResult<SparseArray> {
     let dtype = fill_value.dtype().clone();
     let len = patches.array_len();
+    let patches = SparseData::normalize_patches_dtype(patches, &fill_value)?;
     let slots = SparseData::make_slots(&patches);
-    let data = SparseData::from_patches(&patches, fill_value)?;
+    let data = SparseData::from_patches_unchecked(&patches, fill_value);
     Ok(unsafe {
         Array::from_parts_unchecked(ArrayParts::new(Sparse, dtype, len, data).with_slots(slots))
     })
 }

Linear

ABA-30 — Sparse::try_new_from_patches attaches slots from un-normalized patches.

Validation

• New regression test vortex_sparse::test::issue_aba30_sparse_slot_dtype_matches_declared_dtype fails on develop (slot dtype Primitive(I32, NonNullable) vs array dtype Primitive(I32, Nullable)) and passes after the reorder.
• cargo test -p vortex-sparse — 80 passed, 0 failed.
• cargo clippy -p vortex-sparse --all-targets --all-features — clean.
• cargo +nightly fmt --all -- --check — clean.
• No public API change; public-api.lock unaffected.

Attribution

Co-authored by Claude Opus 4.7 (1M context). Signed-off-by DCO on both commits.