Remove `pyiceberg-core` from the `pyarrow` extra

[kevinjqliu]

Context: apache/iceberg-rust#2442 (comment)

pyiceberg[pyarrow] currently installs both pyarrow and pyiceberg-core. This is too broad: most Arrow read/write paths only need pyarrow, while pyiceberg-core is only used in lazy, feature-specific code paths (native transform kernels, DataFusion table provider).

It also creates a packaging cycle for downstream projects: pyiceberg-core cannot depend on pyiceberg[pyarrow] without re-installing itself through the extra.

[CalebWeisgerber]

I can take a look at this. Quick glance it seems like pyiceberg-core can be removed from the pyarrow dependency but I can remake and check test cases.