fix: compare transform function parameters

[WZhuo]

Summary

• include bucket counts in BucketTransform equality
• include truncate widths in TruncateTransform equality
• cover parameter and source-type differences in transform tests

Testing

• build/src/iceberg/test/schema_test
• pre-commit hooks

[Copilot]

Pull request overview

This PR fixes TransformFunction equality for parameterized transforms so that bucket[N] and truncate[W] comparisons account for their parameters (and source types), and adds tests to prevent regressions.

Changes:

• Make TransformFunction::Equals available to derived classes (protected) for shared equality checks.
• Override Equals in BucketTransform and TruncateTransform to include num_buckets_ / width_ in equality.
• Extend transform tests to cover parameter and source-type differences.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/iceberg/transform.h	Exposes base equality helper (Equals) to derived transforms.
src/iceberg/transform_function.h	Declares equality overrides for bucket/truncate transforms.
src/iceberg/transform_function.cc	Implements parameter-aware equality for bucket/truncate transforms.
src/iceberg/test/transform_test.cc	Adds equality tests for parameter and source-type differences.

[zhjwpku]

Nit: This is only used by the == overload, so maybe we can remove the [[nodiscard]] attribute? Same for the below.

[wgtmac]

Make sense. Thanks @WZhuo for fixing it!