test: add v2.2 format gate regression tests

[Xuanwo]

• add a regression test that rejects writing Blob v2 data with file version 2.1
• add a regression test that rejects FixedSizeList<Struct> encoding with file version 2.1
• add a regression test that ensures requested general compression is not selected for file version 2.1

---

Parts of this PR were drafted with assistance from Codex (with gpt-5.2) and fully reviewed and edited by me. I take full responsibility for all changes.

[github-actions]

Review Summary

LGTM - Clean, well-structured regression tests for v2.2 format gates.

No P0/P1 issues found. The tests properly verify that:

• General compression is not selected for V2.1 even when requested
• FixedSizeList<Struct> encoding is rejected for V2.1
• Blob v2 writes are rejected for V2.1

Minor note: The #[cfg(any(feature = "lz4", feature = "zstd"))] attribute on the compression test is a good practice to avoid test failures when neither compression feature is enabled.

[codecov]

Codecov Report

❌ Patch coverage is 98.43750% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-encoding/src/compression.rs	93.75%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!