ArrayData Equality Incorrect Null Mask Offset Handling

[tustvold]

Describe the bug

The handling of null masks in the ArrayData comparisons does not take into account the ArrayData offset, leading to incorrect results.

To Reproduce

#[test]
fn test_offset() {
    let a = Int32Array::from(vec![Some(1), Some(2), None, Some(0)]);
    let b = Int32Array::from(vec![Some(4), Some(5), Some(0), None]);
    assert_ne!(a.data().slice(2, 2), b.data().slice(2, 2));
}

Expected behavior

The equality comparisons should produce correct results on ArrayData slices