fix: Make ReEDS parser compatible with new cost functions

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.26087% with 27 lines in your changes missing coverage. Please review.

Project coverage is 62.18%. Comparing base (5b5c360) to head (d7bd292).

Files with missing lines	Patch %	Lines
src/r2x/exporter/utils.py	75.51%	12 Missing :warning:
src/r2x/exporter/plexos.py	83.67%	8 Missing :warning:
src/r2x/exporter/sienna.py	93.33%	4 Missing :warning:
src/r2x/models/costs.py	93.33%	2 Missing :warning:
src/r2x/parser/plexos.py	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #44 +/- ## ========================================== + Coverage 60.86% 62.18% +1.32% ========================================== Files 29 29 Lines 3020 3115 +95 ========================================== + Hits 1838 1937 +99 + Misses 1182 1178 -4 ```

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[ktehranchi]

small comments but LGTM