Replace maths library with Python libraries

[timothy-nunn]

Removing some of the maths routines that can be replaced with simple routines from libraries like numpy and scipy.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.88235% with 13 lines in your changes missing coverage. Please review.

Project coverage is 29.53%. Comparing base (ec3c1f5) to head (c6ddd0e).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
process/pfcoil.py	14.28%	12 Missing ⚠️
process/availability.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3418      +/-   ##
==========================================
+ Coverage   29.51%   29.53%   +0.01%     
==========================================
  Files          77       78       +1     
  Lines       19049    20097    +1048     
==========================================
+ Hits         5622     5935     +313     
- Misses      13427    14162     +735     

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[timothy-nunn]

The changes to PF coil require a bit of explaining. The single value decomposition from scipy returns different results to the maths library implementation. This causes the integration tests to fail, but none of the regression tests.

In some cases, like test_solv the values of ccls changed, but their sum did not.
In test_efc, the ccls values changed (one of the PF coils groups ended up with 0 current!?) but the ssq value did not, weirdly, ssq is calculated from the ccls.

Overall, I suspect this is nothing to worry about, but its worth careful consideration before approving.