Convert model initialisation routines to python

[timothy-nunn]

Converts module initialisation (setting of initial defaults) to Python.

In some cases, there was not an obvious places for these functions to live and so I just added to the file that seemed to use the variables the most.

See comment below for the annoying reason there are some slight test changes despite this being a line-for-line port of the code from Fortran to Python.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.38%. Comparing base (03a8c56) to head (d1c9166).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3586      +/-   ##
==========================================
+ Coverage   31.76%   37.38%   +5.62%     
==========================================
  Files          85       85              
  Lines       20175    21983    +1808     
==========================================
+ Hits         6408     8218    +1810     
+ Misses      13767    13765       -2     

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[timothy-nunn]

Errors in the TF coil are being caused by setting

tfv.poisson_cond_axial = 0.3
tfv.poisson_cond_trans = 0.3

The reason
In Fortran, the variables were set like

PROCESS/source/fortran/tfcoil_variables.f90

Lines 929 to 930 in cb982be

	poisson_cond_axial = 0.3
	poisson_cond_trans = 0.3

If you look around, every other float variable being assigned is followed by a D0 which explicitly sets the value to double precision. Therefore, in the Fortran these variables were being initialised to single precision 0.3 (still being assigned to a double precision variable however). When we set 0.3 across the Python-Fortran interface, it does it to double precision not single precision.

To verify, I changed the Fortran code to

poisson_cond_axial = 0.3D0
poisson_cond_trans = 0.3D0

and the same errors (differences) occur as in the Python case.