Bug Fix: Cast UINT32 to INT32 to ensure compatibility with other engines

[JeroenSchmidt]

Rationale for this change

• PyIceberg was preserving original Arrow types in Parquet files, causing Spark to fail with Unsupported logical type: UINT_32
• Extends the integer casting logic in ArrowProjectionVisitor._cast_if_needed to handle unsigned-to-signed conversions at the same bit width. Specifically uint32 -> int32.

Context:

This is a follow-up to #2799 (which fixed #2791) where uint8/uint16 casting was addressed. That fix only covered widening conversions (source_width < target_width), which missed the uint32 case since both uint32 and int32 are 32-bit. Without this cast, Parquet files are written with the UINT_32 physical type while Iceberg metadata declares INT_32, causing Spark to fail on read.

Changes / Are these changes tested?

pyiceberg/io/pyarrow.py: Extended the cast condition to also trigger when the source is an unsigned integer with the same (or smaller) bit width as the signed target
tests/io/test_pyarrow.py: Added (pa.uint32(), IntegerType(), pa.int32()) test case

Notes

• The cast uses PyArrow's default safe=True, so values exceeding INT32_MAX (2^31-1) will raise rather than silently corrupt
• Existing behavior for all other integer type combinations is unchanged