Convert soil + litter exchange variables to be biomass triplets

[jacobcook1995]

Description

This PR changes the remaining variables that pass stoichiometric information into/out of the litter and soil models to use biomass triplets.

The two relevant variables I changed are animal_pom_consumption_* and litter_mineralisation_rate_*. Everything else either wasn't a triplet (e.g. plant_ammonium_uptake or ectomycorrhizal_n_supply and ectomycorrhizal_p_supply) or had already been moved to triplet format

Fixes #1225

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 94.84%. Comparing base (e9763f6) to head (0078964).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1415   +/-   ##
========================================
  Coverage    94.84%   94.84%           
========================================
  Files           71       71           
  Lines         7451     7452    +1     
========================================
+ Hits          7067     7068    +1     
  Misses         384      384           

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[TaranRallings]

Awesome possum.