Fix non-deterministic ordering in ParallelAnalyzer

[ShivamB25]

Fixes #444

Problem

The ParallelAnalyzer produced non-deterministic results due to processing subdirectories in parallel and adding them to the parent directory in completion order rather than filesystem order.

Solution

• Modified processDir to track the original index of all items (both files and directories)
• Both files and subdirectories are now collected with their indices and added to the parent in the original order from os.ReadDir
• Subdirectories are still processed in parallel for performance, but results are reordered before adding

Changes

• Added indexedItem struct to pair items with their original position
• Use buffered channel to collect all items without blocking
• Collect items by index and add in original order

Testing

• Added TestParallelAnalyzerDeterminism: verifies parallel analyzer produces identical results across multiple runs
• Added TestParallelVsSequentialConsistency: verifies parallel and sequential analyzers produce identical results
• Added TestFileDirectoryInterleaving: specifically tests preservation of file/directory ordering
• All existing tests pass

[ShivamB25]

@rafl please verify for the same by having a building yourself of my fork.

[codecov]

Codecov Report

❌ Patch coverage is 77.16535% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.72%. Comparing base (4212583) to head (0d05b34).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/analyze/parallel_stable.go	77.16%	25 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #445      +/-   ##
==========================================
- Coverage   83.88%   83.72%   -0.17%     
==========================================
  Files          46       47       +1     
  Lines        3792     3919     +127     
==========================================
+ Hits         3181     3281     +100     
- Misses        537      561      +24     
- Partials       74       77       +3     

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[dundee]

We need to do proper performance benchmarks for this PR before merging.

[dundee]

I will introduce this as a new analyzer, because there's a performance penalty (approx 1-5%) for keeping the stable sorting.

[ShivamB25]

@dundee i will try to improve the performance.