perf: using Arc<str> to share source content between source map

[SyMind]

This PR optimizes memory usage by changing the internal representation of source content from String to Arc<str> throughout the codebase. This enables efficient string sharing and reduces allocations when the same source content is referenced multiple times.

Key Changes:

• Changed SourceMap::sources_content from Arc<[String]> to Arc<[Arc<str>]>
• Updated OriginalSource::value and SourceMapSource::original_source to use Arc<str> instead of String
• Introduced SourceContentLines struct using the self_cell crate to manage self-referential data structures for cached line splitting

[codspeed-hq]

CodSpeed Performance Report

Merging #196 will improve performances by 13.1%

_{Comparing perf-soruces-content (dd0f92a) with main (c4f7e16)}

Summary

⚡ 1 improvement
✅ 10 untouched
⏩ 5 skipped¹

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	stringify_source_map_to_json	16.6 ms	14.7 ms	+13.1%

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 optimizes memory usage by changing the internal representation of source content from String to Arc<str> throughout the codebase. This enables efficient string sharing and reduces allocations when the same source content is referenced multiple times.

Key Changes:

• Changed SourceMap::sources_content from Arc<[String]> to Arc<[Arc<str>]>
• Updated OriginalSource::value and SourceMapSource::original_source to use Arc<str> instead of String
• Introduced SourceContentLines struct using the self_cell crate to manage self-referential data structures for cached line splitting

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/source_map_source.rs	Updated original_source field type and simplified string conversions using .into()
src/source_content_lines.rs	Added new struct for efficiently managing source content split into lines with self-referential ownership
src/source.rs	Changed sources_content to use Arc<[Arc<str>]> and updated related methods
src/replace_source.rs	Refactored SourceContent enum and helper functions to work with Arc<str> and SourceContentLines
src/original_source.rs	Changed value field to Arc<str> and updated OnSource callback signature
src/lib.rs	Added module declaration for source_content_lines
src/helpers.rs	Updated helper functions, type signatures, and removed unused code
benches/bench.rs	Updated test data initialization to use .into() conversion
Cargo.toml	Added self_cell dependency
Cargo.lock	Added self_cell package entry

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