Restructure remaining process package into process/core

[timothy-nunn]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.41304% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.18%. Comparing base (f7893f0) to head (1b668fd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
process/core/io/plot_proc.py	23.52%	13 Missing ⚠️
process/core/io/mfile_comparison.py	0.00%	2 Missing ⚠️
process/core/io/plot_scans.py	0.00%	2 Missing ⚠️
process/core/io/write_new_in_dat.py	0.00%	2 Missing ⚠️
process/core/io/costs_bar.py	0.00%	1 Missing ⚠️
process/core/io/costs_pie.py	0.00%	1 Missing ⚠️
process/core/io/mfile_to_csv.py	0.00%	1 Missing ⚠️
process/core/io/plot_sankey.py	0.00%	1 Missing ⚠️
process/core/io/plot_solutions.py	0.00%	1 Missing ⚠️
process/core/io/sankey_funcs.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4108   +/-   ##
=======================================
  Coverage   47.18%   47.18%           
=======================================
  Files         138      138           
  Lines       29278    29280    +2     
=======================================
+ Hits        13815    13817    +2     
  Misses      15463    15463           

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