Add comments to nonlinear solver code

[maxpaik16]

Rename compute_collision_free_step_size to compute_max_step_size

Add doxygen style comments to the following headers:

polysolve/nonlinear/Problem.hpp

polysolve/nonlinear/Solver.hpp

polysolve/nonlinear/descent_strategies/DescentStrategy.hpp

polysolve/nonlinear/line_search/LineSearch.hpp

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.54%. Comparing base (97a92c5) to head (9629b82).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #71   +/-   ##
=======================================
  Coverage   87.54%   87.54%           
=======================================
  Files          48       48           
  Lines        2047     2047           
=======================================
  Hits         1792     1792           
  Misses        255      255           

Flag	Coverage Δ
polysolve	87.54% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.