time-varying efficiencies and standing losses for all components

[fneum]

Closes #492.

Changes proposed in this Pull Request

• add unit test for functionality check
• check IO for new series data

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• [ ] Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codecov]

Codecov Report

Patch coverage: 96.29% and project coverage change: +0.92 🎉

Comparison is base (be05f3c) 75.61% compared to head (1790ecf) 76.54%.

❗ Current head 1790ecf differs from pull request most recent head 241a141. Consider uploading reports for the commit 241a141 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #572      +/-   ##
==========================================
+ Coverage   75.61%   76.54%   +0.92%     
==========================================
  Files          24       24              
  Lines        6246     6258      +12     
  Branches     1336     1336              
==========================================
+ Hits         4723     4790      +67     
+ Misses       1240     1186      -54     
+ Partials      283      282       -1     

Impacted Files	Coverage Δ
pypsa/pf.py	83.47% <83.33%> (+0.05%)	⬆️
pypsa/linopf.py	80.35% <100.00%> (+0.17%)	⬆️
pypsa/opf.py	89.78% <100.00%> (+0.22%)	⬆️
pypsa/optimization/constraints.py	91.68% <100.00%> (ø)
pypsa/optimization/global_constraints.py	87.15% <100.00%> (+0.05%)	⬆️

... and 2 files with indirect coverage changes

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[FabianHofmann]

This is great, can we rename test/test_lopf to something more specific? test_lopf_varying_inputs?

[fneum]

Done.