IO: Consolidate PyArrow logic into io/pyarrow.py before decomposition

まず table/upsert_util.py と pyiceberg/io/pyarrow.py を比較し、#3737 の関連する議論を確認してください。最初に PR A に取り組みます。完了とは、upsert utility の PyArrow ロジックが io/pyarrow.py を経由し、動作を変更せず、既存のすべてのテストに合格することを意味します。

Summary

Before decomposing pyiceberg/io/pyarrow.py into focused submodules (#3737, #3738), we should consolidate PyArrow-specific logic that currently lives outside the module. This ensures all PyArrow calls route through a single boundary, making the subsequent split clean and enabling future engine substitution.

Motivation

Per discussion in #3737, @rambleraptor noted that the first useful step is ensuring no PyArrow logic occurs outside pyarrow.py. Currently several modules import pyarrow directly and implement compute logic inline rather than delegating through pyiceberg.io.pyarrow.

When we later introduce a ComputeEngine protocol, any PyArrow logic outside the module boundary bypasses the protocol and prevents clean substitution.

Audit

Grepped pyiceberg/ (excluding io/pyarrow.py and tests) for runtime import pyarrow statements (both top-level and inline). Excluded TYPE_CHECKING-only imports since those have no runtime dependency.

Plan

One PR per absorption. Each is a pure refactor: move code into io/pyarrow.py, have the caller import from pyiceberg.io.pyarrow instead of pyarrow directly. No behavior change, all existing tests pass unchanged.

• PR A: Absorb table/upsert_util.py PyArrow logic
• PR B: table/inspect.py (pending discussion)
• PR C: transforms.py (pending discussion)

Related

• #3737 - Decompose io/pyarrow.py into focused modules
• #3738 - Extract PyArrowFileIO (first decomposition step)
• #3715 / #3716 - Previous pluggable backend attempt (rejected as too large)