IO: Extract PyArrowFileIO into dedicated module

[qzyu999]

Summary

Extract PyArrowFile, PyArrowFileIO, PyArrowLocalFileSystem and their helper functions into a new pyiceberg/io/_pyarrow_fileio.py module. The original pyiceberg/io/pyarrow.py re-exports all public names for full backward compatibility.

This is the first step toward decomposing the 3,100+ line pyarrow.py monolith into focused modules by concern (tracked in #3737).

Changes

• New file: pyiceberg/io/_pyarrow_fileio.py (584 lines) containing the FileIO implementation
• Modified: pyiceberg/io/pyarrow.py (-537 lines) replaced inline definitions with re-exports
• Removed unused imports from pyarrow.py that were only needed by the FileIO section

What stays the same

• All existing from pyiceberg.io.pyarrow import PyArrowFileIO imports continue to work
• Zero behavior change pure code movement with re-exports
• Pickle/unpickle of PyArrowFileIO works unchanged
• No new dependencies

Why

pyarrow.py handles 6 unrelated concerns in one file. The FileIO concern (filesystem abstraction for S3/GCS/Azure/HDFS/local) has zero coupling to schema conversion, expression translation, or statistics collection. Extracting it:

1. Reduces cognitive load when working on scan/write logic
2. Establishes the pattern for subsequent extractions (schema, expressions, stats, write, scan)
3. Creates a clean seam point for future alternative FileIO implementations

Testing

Full unit test suite passes: 3803 passed, 3 skipped, 0 failures, 0 errors

(Windows local testing requires #3721 + #3722 applied on top; Linux CI should pass without them.)