Minor Power Plant Costing Fixes

[bpaul4]

Fixes

Minor modifications to power plant costing.

Changes proposed in this PR:

• correct units on a couple of terms
• set additional_cost_of_electricity to initialize at 0, add details to docstring
• fix transport_cost units and handling

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 76.35%. Comparing base (85bf669) to head (1f828e4).
Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
...ra/power_generation/costing/power_plant_capcost.py	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1418      +/-   ##
==========================================
- Coverage   76.36%   76.35%   -0.01%     
==========================================
  Files         394      394              
  Lines       64953    64953              
  Branches    14404    14404              
==========================================
- Hits        49601    49598       -3     
- Misses      12793    12797       +4     
+ Partials     2559     2558       -1     

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[AlexNoring]

lgtm

[dallan-keylogic]

LGTM