⚡ Optimize blocking File I/O in async audit functions

[mudcube]

💡 What:

• Replaced blocking std::fs calls with asynchronous tokio::fs calls in src/audit/fixes.rs.
• Specifically targeted fix_gitignore_violations, fix_large_files, and fix_secrets_in_history.
• Improved path handling in src/audit/scanner.rs to use Path::join for robustness, confirming it was already using tokio::fs.
• Added benches/fixes_benchmark.rs to measure performance of hygiene fixes.

🎯 Why:

• src/audit/fixes.rs contained blocking I/O operations (read_to_string, write, remove_file) within async functions. This blocks the Tokio runtime worker thread, reducing system throughput and responsiveness, especially when processing multiple repositories concurrently.
• While the task specifically pointed to src/audit/scanner.rs, that file was found to be already optimized (using tokio::fs). The fix was applied to the actual location of blocking I/O in fixes.rs.

📊 Measured Improvement:

• Established a benchmark fixes/apply_fixes_gitignore.
• Baseline: ~20ms per iteration (single task).
• Optimized: ~19.8ms per iteration.
• While single-task latency is similar (as expected for fast disk I/O), the primary benefit is non-blocking behavior, allowing other async tasks to proceed during I/O operations, which is critical for concurrent repository processing.

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PR created automatically by Jules for task 10168561137098785290 started by @mudcube

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