Implement RobustArmijo and refactor Armijo Line Search

[zfergus]

• Implement the numerically robust Armijo line search of Longva et al. [2023]

TODO:

• Re-enable use_grad_norm
• Only compute new_grad as needed

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (49edbec) 89.12% compared to head (c2656a1) 89.01%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/polysolve/nonlinear/line_search/LineSearch.cpp	72.22%	5 Missing ⚠️
...c/polysolve/nonlinear/line_search/Backtracking.cpp	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
- Coverage   89.12%   89.01%   -0.12%     
==========================================
  Files          49       51       +2     
  Lines        1950     1948       -2     
==========================================
- Hits         1738     1734       -4     
- Misses        212      214       +2     

Flag	Coverage Δ
polysolve	89.01% <89.23%> (-0.12%)	⬇️

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