782 abiotic model relative humidity is 100 we need to include some form of advectionoutlet

[vgro]

This PR adds vertical mixing of water below the canopy and ventilation above the canopy so water can leave the system. The unit tests create nice vertical humidity profiles, however, the integrated function still returns 100% humidity. I think this has to do with the time interval and the input values and will likely become more realistic when we do the calibration. Any insight are welcome.

I also did a bit of a tidy in the test files, can be skipped.
Fixes #782

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 94.27%. Comparing base (e09cf06) to head (45e03bc).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #957      +/-   ##
===========================================
+ Coverage    94.24%   94.27%   +0.03%     
===========================================
  Files           79       79              
  Lines         6477     6511      +34     
===========================================
+ Hits          6104     6138      +34     
  Misses         373      373              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jacobcook1995]

LGTM (with the obvious caveat that I don't understand the underlying science that well)