PEtab parameter mapping: minor speedup

[dweindl]

Avoid repeated lookups. Saves just a few seconds for Froehlich_CellSystems2018, but better than nothing...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.04%. Comparing base (923b8f4) to head (d0ce54b).
Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2640      +/-   ##
===========================================
- Coverage    77.06%   77.04%   -0.03%     
===========================================
  Files          332      332              
  Lines        22972    22974       +2     
  Branches      1478     1478              
===========================================
- Hits         17704    17700       -4     
- Misses        5257     5263       +6     
  Partials        11       11              

Flag	Coverage Δ
cpp	74.14% <16.66%> (-0.04%)	⬇️
cpp_python	33.47% <16.66%> (-0.01%)	⬇️
petab	38.88% <100.00%> (+0.01%)	⬆️
python	72.12% <66.66%> (-0.03%)	⬇️

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Files with missing lines	Coverage Δ
python/sdist/amici/petab/conditions.py	96.29% <100.00%> (+0.80%)	⬆️
python/sdist/amici/petab/util.py	80.95% <100.00%> (ø)

... and 2 files with indirect coverage changes