perf: object pool

[SyMind]

This PR introduces a ObjectPool system to optimize memory allocations by reusing Vec<usize> buffers, particularly for the WithIndices struct. The pool uses a BTreeMap to organize vectors by capacity and only pools vectors with capacity ≥ 64 elements to balance pooling benefits with overhead.

• Adds ObjectPool and Pooled for efficient vector reuse
• Threads memory_pool parameter through the StreamChunks trait and all implementations
• Updates WithIndices to use pooled vectors instead of regular Vec<usize>

[codspeed-hq]

CodSpeed Performance Report

Merging #192 will improve performances by 20.83%

_{Comparing memory-pool (6ddd2b1) with main (98db0a7)}

Summary

⚡ 2 improvements
✅ 9 untouched
⏩ 5 skipped¹

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	complex_replace_source_map	51.6 ms	42.7 ms	+20.83%
⚡	repetitive_react_components_map	2.6 ms	2.2 ms	+15.68%

Footnotes

1. 5 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[Copilot]

Pull Request Overview

This PR introduces a MemoryPool system to optimize memory allocations by reusing Vec<usize> buffers, particularly for the WithIndices struct. The pool uses a BTreeMap to organize vectors by capacity and only pools vectors with capacity ≥ 64 elements to balance pooling benefits with overhead.

• Adds MemoryPool and PooledUsizeVec for efficient vector reuse
• Threads memory_pool parameter through the StreamChunks trait and all implementations
• Updates WithIndices to use pooled vectors instead of regular Vec<usize>
• Refactors MapOptions to manually implement PartialEq, Eq, and Hash traits

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/memory_pool.rs	Introduces new memory pool infrastructure with MemoryPool and PooledUsizeVec types
src/with_indices.rs	Updates to use PooledUsizeVec instead of Vec<usize> with lifetime parameter changes
src/source.rs	Adds manual trait implementations for MapOptions and threads memory_pool parameter through StreamChunks
src/helpers.rs	Updates all streaming functions to accept and pass through memory_pool parameter
src/source_map_source.rs	Threads memory_pool parameter and creates default pool where needed
src/replace_source.rs	Updates to use memory_pool when creating WithIndices instances
src/raw_source.rs	Adds memory_pool parameter to StreamChunks implementations (unused)
src/original_source.rs	Adds memory_pool parameter to StreamChunks implementation (unused)
src/concat_source.rs	Threads memory_pool parameter through nested stream_chunks calls
src/cached_source.rs	Threads memory_pool parameter and updates tests
src/lib.rs	Exports new MemoryPool type
tests/compat_source.rs	Updates test implementation to match new StreamChunks signature

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