Add an expression that covers both simple and compact methods

[gnawin]

Pull request details

Describe the changes made in this pull request

• Add new expression that is either accumulate_capacity_simple_method or accumulate_capacity_compact_method depending on the asset. For the latter, sum over all v, following the method used for the capacity constraint.
• Sum all vintage years to get the total initial units for simple method
• Change names from accumulated_capacity* to accumulated_units*

List of related issues or pull requests

Closes #798

Collaboration confirmation

As a contributor I confirm

• I read and followed the instructions in README.dev.md
• The documentation is up to date with the changes introduced in this Pull Request (or NA)
• Tests are passing
• Lint is passing

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (21650c1) to head (13094ac).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #800   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           18        18           
  Lines          961       964    +3     
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+ Hits           961       964    +3     

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[datejada]

LGTM, let's wait, if @abelsiqueira has comments on the code

[abelsiqueira]

LGTM