Fixing LUE and units in pmodel

[davidorme]

Description

• The light use efficiency reported by the P Model can be undefined in some extreme conditions. This results in np.nan values that propagate down to the soil model integration, which crashes the simulation (Maliau simulation fails #1314). This is now fixed by using np.nan_to_num to force zero LUE under those conditions.
• The PModel fitting was using VPD and PATM straight out of the data in kPa and pyrealm.PModel requires Pascals. Essentially the plants were growing in an incredibly humid near vacuum.
• The PR also restructures the estimate_gpp - it was doing a lot of subsetting the vertical layers down to the canopy layers and it seems much more straightforward to pad the canopy layers out to the full vertical layers.

Fixes #1354

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 94.87%. Comparing base (8a26398) to head (e29a057).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1362      +/-   ##
===========================================
+ Coverage    94.85%   94.87%   +0.01%     
===========================================
  Files           71       71              
  Lines         7387     7388       +1     
===========================================
+ Hits          7007     7009       +2     
+ Misses         380      379       -1     

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[vgro]

Looks like a sensible fix to me, I just have a few minor comments, most important one that the output to data needs to have the nan values back.

[vgro]

LGTM