fix(spec): implement Display for BinaryTableStats

[u70b3]

Purpose

Linked issue: close #631

The Display impl for BinaryTableStats in spec/stats.rs is the repository's only todo!() and would panic if any code path ever formats stats through Display (logging, debugging, error messages). This implements it.

Brief change log

Implement Display for BinaryTableStats as a labeled summary, following the convention of DataFileMeta's Display:

BinaryTableStats{minValues=[0, 0, 0, 2, 1], maxValues=[0, 0, 0, 2, 9], nullCounts=[Some(0), None, Some(3)]}

• min_values/max_values are serialized BinaryRows that cannot be decoded without the column types, so they print as raw bytes — the same convention DataFileMeta uses for its minKey/keyStats fields.
• null_counts items are Option<i64> (None = unknown), which {:?} renders naturally.

Assumptions and notes for reviewers

• No current caller formats stats via Display: ManifestFileMeta and DataFileMeta print BinaryTableStats fields via {:?} (Debug), so this change is preventive — it removes a panic landmine rather than fixing a live crash. The alternative (deleting the unused impl) was considered and rejected: BinaryTableStats is a public spec-layer type and Display is a basic debugging capability, so implementing it is the additive, non-breaking choice.
• The output format is a proposal: raw bytes mirror the DataFileMeta convention; a byte-length summary (e.g. minValues=12 bytes) would also work. Happy to switch if reviewers prefer.

Tests

• spec::stats::tests::display_formats_labeled_fields — exact output for known bytes, including Some/None null-count mixes
• spec::stats::tests::display_empty_stats_does_not_panic — BinaryTableStats::empty() boundary case

cargo test -p paimon --lib spec:: passes (450 tests); cargo fmt and clippy are clean.

API and Format

No API or storage format change; this fills in a previously unimplemented trait method.

Documentation

No documentation update needed.

🤖 Generated with Claude Code

[QuakeWang]

+1