Fix truncate transform ordering comparison

[mattfaltyn]

Closes #3680

Rationale for this change

TruncateTransform.satisfies_order_of accessed the uninitialized _source_type attribute when comparing truncate transforms with different widths, raising AttributeError instead of returning a boolean.

Compare truncate widths directly, consistent with the Apache Iceberg Java implementation.

Are these changes tested?

Yes. Added regression coverage for both wider-to-narrower and narrower-to-wider comparisons.

• uv run python -m pytest tests/test_transforms.py -q (283 passed)
• make lint
• make test PYTEST_ARGS=-q (3,768 passed; 1,560 deselected)

Are there any user-facing changes?

Yes. Comparing truncate transforms with different widths now returns the expected boolean instead of raising AttributeError.

[github-actions]

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