refactor(btree): optimize BTreeFileMetaSelector with zero-copy comparator

[lxy-9602]

Purpose

Linked issue: #38

Optimize BTreeFileMetaSelector key comparison to use zero-copy MemorySlice comparator,
consistent with BTreeGlobalIndexReader.

• Replace DeserializeKey + Literal::CompareTo with MemorySlice::SliceComparator
• Use MemorySegment::WrapView for non-copying key slices

Tests

API and Format

Documentation

Generative AI tooling

Generated-by: Claude-4.6-Opus

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR refactors BTreeFileMetaSelector to speed up key comparisons by switching from Literal deserialization/comparison to a zero-copy MemorySlice comparator, aligning the comparison approach with BTreeGlobalIndexReader.

Changes:

• Introduce a cached MemorySlice::SliceComparator in BTreeFileMetaSelector.
• Replace DeserializeKey + Literal::CompareTo with SerializeLiteral + MemorySlice comparator calls.
• Add WrapKeySlice to build non-owning key slices from stored key bytes.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/paimon/common/global_index/btree/btree_file_meta_selector.h	Adds MemorySlice comparator support and new helper APIs (SerializeLiteral, WrapKeySlice).
src/paimon/common/global_index/btree/btree_file_meta_selector.cpp	Switches all predicate comparisons to MemorySlice comparator and implements the new slice helpers.

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