Remove use of warnings.warn

[je-cook]

Description

Closes #4402

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 42.30769% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.83%. Comparing base (024a2f2) to head (2a3b456).

Files with missing lines	Patch %	Lines
process/core/init.py	33.33%	10 Missing ⚠️
process/core/caller.py	0.00%	1 Missing ⚠️
process/core/input.py	66.66%	1 Missing ⚠️
process/core/io/plot/solutions.py	0.00%	1 Missing ⚠️
process/core/solver/iteration_variables.py	66.66%	1 Missing ⚠️
process/models/tfcoil/quench.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4407   +/-   ##
=======================================
  Coverage   48.83%   48.83%           
=======================================
  Files         151      151           
  Lines       29397    29397           
=======================================
  Hits        14356    14356           
  Misses      15041    15041           

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