feat: sort order

[zhjwpku]

No description provided.

[Copilot]

Pull Request Overview

This PR adds functionality for sorting by implementing new SortOrder and SortField classes along with comprehensive tests.

• Implements SortOrder and SortField classes with formatting and equality comparison.
• Provides tests to validate sort order behavior and proper string output.
• Adds a custom TransformFunction for testing purposes.

Reviewed Changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/sort_order_test.cc	Adds tests for basic functionality and equality for SortOrder.
test/sort_field_test.cc	Adds tests for basic functionality and equality for SortField.
src/iceberg/sort_order.h	Declares the SortOrder class with defined formatting and equality.
src/iceberg/sort_order.cc	Implements SortOrder with string formatting and equality check.
src/iceberg/sort_field.h	Declares the SortField class with string formatting and equality.
src/iceberg/sort_field.cc	Implements SortField with formatting and equality check.

Files not reviewed (2)

• src/iceberg/CMakeLists.txt: Language not supported
• test/CMakeLists.txt: Language not supported

[wgtmac]

LGTM

[zhjwpku]

@Fokko @Xuanwo Please take a look at this PR when you are available, thanks ;)

[wgtmac]

Do you have any comment? @lidavidm

[Fokko]

Thanks @zhjwpku for working on this, and thanks @wgtmac, @lidavidm and @gty404 for the reviews 🙌