Summary variables calculated only when called

[pipliggins]

Description

Rather than calculating summary variables and storing them in every Solution class, a 'SummaryVariables' class is created which stores the first + last state of the solution, plus any relevant esoh parameters, so that the summary variables are only calculated and stored when they are called (similar to accessing standard variables). If an esoh variable is requested, they are all calculated and stored at once to reduce the number of calls to the esoh solver.

rather than viewing the list of summary variable names as

sol.summary_variables.keys()

you can now use

sol.summary_variables.all_variables

to view the names without calculating the variables.

Similarly, when plotting rather than getting the number of cycles as

sol.summary_variables['Cycle number']

they are accessed as

sol.summary_variables.cycle_number

Fixes #4058

Type of change

• Optimization (back-end change that speeds up the code)

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: $ python run-tests.py --all (or $ nox -s tests)
• The documentation builds: $ python run-tests.py --doctest (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ python run-tests.py --quick (or $ nox -s quick).

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.22%. Comparing base (55dd848) to head (bed5ae9).
Report is 131 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4621      +/-   ##
===========================================
+ Coverage    99.09%   99.22%   +0.12%     
===========================================
  Files          302      303       +1     
  Lines        22992    22955      -37     
===========================================
- Hits         22783    22776       -7     
+ Misses         209      179      -30     

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[rtimms]

related: #4619

[martinjrobins]

sorry for the delay in the review! This looks great, can you please add to the CHANGELOG under breaking changes, since this changes the api for the summary variables?

[martinjrobins]

looks good, thanks @pipliggins