add hmat/mat product, h-lu and h-cholesky + ruff clean

[PierreMarchand20]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.69%. Comparing base (18eb16c) to head (e37d075).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #16 +/- ##
==========================================
+ Coverage 99.39% 99.69% +0.29% 
==========================================
Files 28 28 Lines 661 655 -6 ==========================================
- Hits 657 653 -4 + Misses 4 2 -2 

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