Explicitly release the GIL on calls to the pardiso

[jcapriot]

Explicitly release the GIL on calls to the pardiso functions.

I had thought this was already working, however all we did by adding nogil to the function declaration, e.g.

cdef _run_pardiso(self, ....) nogil:

was declare that it could be ran without the GIL. In order to release the GIL in Cython you need to explicitly release it in a context manager. As explained in the Cython documentation here.

So I've now done through and explicitly released the GIL on all calls to the pardiso C functions.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 40.49%. Comparing base (c48ea7e) to head (2c66ce6).
Report is 3 commits behind head on main.

Files	Patch %	Lines
pydiso/mkl_solver.pyx	0.00%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #14       +/-   ##
===========================================
- Coverage   74.78%   40.49%   -34.30%     
===========================================
  Files           2        3        +1     
  Lines         238      363      +125     
  Branches        0       18       +18     
===========================================
- Hits          178      147       -31     
- Misses         60      214      +154     
- Partials        0        2        +2     

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