Feat/plexos parser xml

[JensZack]

Update the plexos parser to find a single xml file in the run_directory when available. If the fmap is provided that will be used in favor of finding the only xml file. When multiple xml files are present, this will raise an Error, and then the fmap will be required again.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.07%. Comparing base (3caade5) to head (c6379b3).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/r2x/parser/plexos_utils.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #93      +/-   ##
==========================================
+ Coverage   73.98%   74.07%   +0.08%     
==========================================
  Files          37       37              
  Lines        3729     3745      +16     
==========================================
+ Hits         2759     2774      +15     
- Misses        970      971       +1     

Files with missing lines	Coverage Δ
src/r2x/parser/plexos.py	53.13% <100.00%> (+0.21%)	⬆️
src/r2x/parser/plexos_utils.py	61.85% <91.66%> (+1.96%)	⬆️

[pesap]

LGTM!