some tests/ too-many-statements quality fixes + tidying

[clmould]

Description

Some more improve-quality-test fixes on tests/ files to remove the 'too-many-statements'

tests for stellerator, dcll, buildings, power, costs_1990

Also general tidying by removing unused monkeypatch params (either not used in the fn being tested, or are directly calculated in the fn being tested and then the output is checked so no need to monkeypatch in the first place)

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.85%. Comparing base (ddcba6c) to head (68beb10).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4382   +/-   ##
=======================================
  Coverage   48.85%   48.85%           
=======================================
  Files         151      151           
  Lines       29385    29385           
=======================================
  Hits        14356    14356           
  Misses      15029    15029           

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