Execution order based on variables

[dalonsoa]

Description

Replaces the current calculation of the model execution order in init and update - based on the input configuration - with another one based on the information on which variables each model initialises and which ones they require.

Using this method has identified also an inconsistency in the variables used by the soil model, which I guess it is a good thing!

The depends section of the example config files have been removed, and I had not spotted it being mentioned anywhere else, including the documentation, but let me know if I missed anything.

In principle, this is the last bit of the implementation of the variables system.

Fixes #389

Type of change

• 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

• Make sure you've run the pre-commit checks: $ pre-commit run -a
• All tests pass: $ poetry run pytest

Further checks

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.05%. Comparing base (8097392) to head (2842194).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #548   +/-   ##
========================================
  Coverage    95.04%   95.05%           
========================================
  Files           74       74           
  Lines         4262     4269    +7     
========================================
+ Hits          4051     4058    +7     
  Misses         211      211           

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[jacobcook1995]

LGTM!

[vgro]

LGTM