refactor(file_system): deduplicate read methods and use Vec<u8>

[Boshen]

Summary

Refactors the FileSystem trait to eliminate code duplication and improve maintainability:

• Added read() method returning Vec<u8> as the primary file reading method
• Deduplicated read_to_string() to call read() + UTF-8 validation
• Removed read_to_string_bypass_system_cache() method (simplified API)
• Updated PackageJson::parse() to work with Vec<u8> instead of String

🤖 Generated with Claude Code

[graphite-app]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.26%. Comparing base (aa90a41) to head (6b1c9ed).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #816      +/-   ##
==========================================
- Coverage   94.40%   94.26%   -0.14%     
==========================================
  Files          17       17              
  Lines        3074     3071       -3     
==========================================
- Hits         2902     2895       -7     
- Misses        172      176       +4     

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[codspeed-hq]

CodSpeed Performance Report

Merging #816 will not alter performance

_{Comparing refactor/deduplicate-filesystem-read (6b1c9ed) with main (aa90a41)¹}

Summary

✅ 10 untouched
⏩ 5 skipped²

Footnotes

1. No successful run was found on main (6b1c9ed) during the generation of this report, so aa90a41 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 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. ↩

[Boshen]

Merge activity

• Nov 6, 10:53 AM UTC: The merge label 'merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Nov 6, 10:53 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Nov 6, 10:57 AM UTC: Merged by the Graphite merge queue.