Add scipy and nlopt SLSQP solvers

[jonmaddock]

Add interfaces to scipy and nlopt's SLSQP implementations.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 10.36585% with 147 lines in your changes missing coverage. Please review.

Project coverage is 37.93%. Comparing base (9064b51) to head (7526116).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
process/solver.py	10.36%	147 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3684      +/-   ##
==========================================
+ Coverage   36.99%   37.93%   +0.94%     
==========================================
  Files          84       88       +4     
  Lines       21688    22634     +946     
==========================================
+ Hits         8023     8587     +564     
- Misses      13665    14047     +382     

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