Optimize computations in LBFGS

[MaxenceGollier]

#378

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.13%. Comparing base (32dbc5e) to head (623203a).
⚠️ Report is 48 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #381      +/-   ##
==========================================
- Coverage   95.00%   94.13%   -0.87%     
==========================================
  Files          17       20       +3     
  Lines        1100     1143      +43     
==========================================
+ Hits         1045     1076      +31     
- Misses         55       67      +12     

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