Bag of little bootstrap

[aisa6148]

Refactor LensKit Statistical Components and Fix Ray Tests

Changes

1. Statistical Module Reorganization

• Moved argtopn from lenskit.stats to lenskit.data.types
• Removed duplicate implementation from stats.base
• Updated all imports

2. Gini Implementation

• Moved Gini implementation to base.py

3. BLB (Bag of Little Bootstraps) Improvements

• Fixed parallel processing tests
• Added ignore_reinit_error=True to Ray initialization
• Improved test stability and reliability

No. of files changed: 10

[codecov]

Codecov Report

❌ Patch coverage is 97.11538% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.42%. Comparing base (16e5fc7) to head (9060f8a).
⚠️ Report is 145 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lenskit/stats/blb.py	96.10%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #786      +/-   ##
==========================================
+ Coverage   90.39%   90.42%   +0.02%     
==========================================
  Files         150      152       +2     
  Lines       10592    10675      +83     
==========================================
+ Hits         9575     9653      +78     
- Misses       1017     1022       +5     

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[mdekstrand]

Kluver is helping debug #787, and we'll use that one as the basis for the version to merge (if we can get it working). Thank Thanks for working on this!