Move `_determine_partitions` to `pyarrow.py`

### Feature Request / Improvement

It relies heavily on PyArrow, so it should be in `pyarrow.py` as suggested by @HonahX in https://github.com/apache/iceberg-python/pull/569#discussion_r1659979992