fix(arrow): deep-copy the right rows from a sliced boolean column

[MaxFreedomPollard]

deep_copy_array_data_sliced in rust/lance-arrow/src/deepcopy.rs copied from the wrong place: mutable.extend(0, data.offset(), data.offset() + data.len()). MutableArrayData::extend already indexes from the source array's first logical element. ArrayData::buffer hands the value extenders a slice that starts at self.offset, and the null-bit extender adds nulls.offset() itself. Passing the offset in as start applies it a second time, so the copy begins offset elements past the slice.

Most arrays hide this, because to_data() folds a slice into the buffer pointer and leaves ArrayData::offset at 0. A boolean array cannot: a bit offset has no byte pointer to fold into, so From<BooleanArray> for ArrayData sets .offset(array.values.offset()) and a sliced boolean column keeps a non-zero offset. Its deep copy comes back shifted by that many bits, values and validity alike.

Two public entry points reach it. RecordBatchExt::shrink_to_fit is a direct call into deep_copy_batch_sliced. And rechunk_stream_by_size_deep_copy deep-copies every slice it produces, which is how HardCapBatchSizeExec caps batch sizes ahead of a DataFusion sort, so a large batch with a boolean column comes back through that node with the wrong booleans and no error.

The fix is to copy from 0. The regression test slices a boolean array that has nulls at offset 3, asserts the slice really does carry ArrayData::offset == 3, and compares the copy against the slice element by element.

Verification, run from rust/ on 1.97.0:

cargo test -p lance-arrow passes, 102 unit tests and 6 doctests. Reverting just the one-line fix and keeping the test makes test_deep_copy_array_sliced_boolean_keeps_offset fail with left: [Some(true), Some(false), Some(true), Some(true)] against right: [Some(true), Some(true), Some(false), Some(true)], while the five deepcopy tests that were already there still pass, which is why this went unnoticed.

cargo clippy -p lance-arrow --all-targets --all-features -- -D warnings is clean, and so is cargo fmt --all -- --check.

[lance-gatekeeper]

✅ Gate recommendation: approve.

The fix restores the logical-slice contract: MutableArrayData::extend receives 0..len, so non-zero-offset boolean values and validity are copied once into compact buffers. The regression test covers the offset case, and the shared copy path remains correct for existing array types.