Update simulation class private members

[BradyPlanden]

Description

A small PR to remove usage of the simulation class properties, within the class.

Fixes # (issue)

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

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

[valentinsulzer]

Don't see any problem with doing this but what is wrong with the other way out of interest?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.50%. Comparing base (58bbf13) to head (2ca8fe8).
Report is 162 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4319   +/-   ##
========================================
  Coverage    99.50%   99.50%           
========================================
  Files          289      289           
  Lines        22146    22146           
========================================
  Hits         22037    22037           
  Misses         109      109           

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[BradyPlanden]

Fair question, I'd say it mainly removes confusion for developers and users looking through the codebase. Since the attributes I've corrected were using the property, we're presenting these objects as modifiable outside the class without issues, which is not the case (or if it is, we can remove them as private attrs and the corresponding properties) while also having the private attributes used elsewhere in the class (i.e. mixing them up throughout the class).

This actually came from a PyBOP PR, as we are using a few of the simulation class methods during build. One of the attributes (self.model) uses both the property and the private attribute, so we needed to do this in one spot. This will clean things up for both packages.

As a side note, PyBOP is moving towards doing this automatically with ruff: pybop-team/PyBOP#435 I suspect doing something similar would be beneficial for PyBaMM as well; however, it takes a bit of work to fix everything at the beginning..

[valentinsulzer]

Thanks for the info, definitely sounds like a useful check to include