fix(io): keep null lists of structs when projecting Arrow data

[DG47]

Closes #3833

Rationale for this change

ArrowProjectionVisitor.list rebuilds a list whose element is a struct with pa.LargeListArray.from_arrays(list_array.offsets, value_array). The offsets alone cannot express a null list, so every null list<struct<...>> came out as an empty list. The visitor runs on both the read and the write path; on write the empty list is persisted into the Parquet file, so the null is gone for every reader, not only for pyiceberg.

Reproduction from the issue (pyarrow 25.0.1):

l_struct  in=[[{'x': 1}], [], None, [{'x': 3}]]  out=[[{'x': 1}], [], [], [{'x': 3}]]
l_int     in=[[1], [], None, [3]]                out=[[1], [], None, [3]]

This PR rebuilds the list with pa.Array.from_buffers, reusing the validity and offsets buffers (and the array offset) of the original list and swapping in the projected element array. Passing mask=list_array.is_null() to from_arrays would fix the unsliced case, but Arrow rejects a mask together with sliced offsets (Null bitmap with offsets slice not supported) for LargeListArray, so sliced batches would start raising. Reusing the buffers keeps the array offset and avoids that.

The integration test test_null_list_and_map asserted the corrupted value with the correct assertion commented out; the correct assertion is restored.

Are these changes tested?

• New unit test test__to_requested_schema_null_list_of_structs in tests/io/test_pyarrow.py, parametrized over pa.list_ and pa.large_list, covering a full batch and a sliced one. It fails on main (At index 2 diff: [] != None) and passes with this change.
• Restored the real assertion in tests/integration/test_reads.py::test_null_list_and_map.
• make test and make lint pass locally.

Are there any user-facing changes?

Null lists of structs are now preserved on read and write instead of being turned into empty lists.