Use Clarabel instead of OSQP to solve QPP in VMCON

[timothy-nunn]

I am noticing some non-determinisim in solver (specifically for the spherical tokamak regression test) where an "inaccurate solution" is returned from OSQP and this results in a non-deterministic step length. Clarbel was recommended for its determinism and accuracy (osqp/osqp-python#116)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.05%. Comparing base (5eeaeff) to head (42c55e4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3971   +/-   ##
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  Coverage   46.05%   46.05%           
=======================================
  Files         123      123           
  Lines       28737    28738    +1     
=======================================
+ Hits        13234    13235    +1     
  Misses      15503    15503           

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[timothy-nunn]

The use of Clarabel does not have an impact on convergence compared to current PROCESS:

These are the results of running 2000 input files within +/-30% of the starting position of the ST and LT-NOF regression tests (1000 from each test).