compute_output_current in system base

[m-bossart]

To match postprocessing methods for other models, compute_output_current should always return currents in the system base for StandardLoad, PowerLoad, and ExponentialLoad . This change removes the dependency on the units setting of the system.

[codecov]

Codecov Report

Merging #351 (c292d27) into main (deffaae) will increase coverage by 0.10%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #351      +/-   ##
==========================================
+ Coverage   87.30%   87.40%   +0.10%     
==========================================
  Files          65       65              
  Lines        8986     8995       +9     
==========================================
+ Hits         7845     7862      +17     
+ Misses       1141     1133       -8     

Flag	Coverage Δ
unittests	87.40% <100.00%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
src/post_processing/post_proc_loads.jl	97.19% <100.00%> (+14.54%)	⬆️

... and 1 file with indirect coverage changes

[github-actions]

Performance Results

Version	Precompile Time
Main	5.115656155
This Branch	5.258909785

Version	Execute Time
Main-Build ResidualModel	13.377871785
Main-Execute ResidualModel	34.080619047
Main-Build MassMatrixModel	1.137557307
Main-Execute MassMatrixModel	360.984364024
This Branch-Build ResidualModel	13.168182354
This Branch-Execute ResidualModel	35.892133313
This Branch-Build MassMatrixModel	1.131606052
This Branch-Execute MassMatrixModel	356.954510069

ResidualModel and MassMatrixModel performance results should be compared between versions and not between models due to the execution order of the tests

[m-bossart]

Doesn't hit the codecov target because the method for PowerLoad is not tested. Is PowerLoad still supported? Should I add a test for PowerLoad?