Allow P Models to accept an array of kphio values

[davidorme]

Description

This PR update the kphio arguments to PModel and SubdailyPModel to accept an array of kphio estimates. This is largely intended to allow users to test alternative models for calculating kphio - there is an approach that accounts for temperature and soil moisture being developed.

The PR then includes a new test suite for this feature that checks that outcomes of passing in an array of kphio values is identical to the predictions of calculating those values using a single value at a time, and that the results are not sensitive to the shape of the inputs. That is repeated for PModel and SubdailyPModel.

Fixes #261

Type of change

• [x] 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

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

Further checks

• [x] Code is commented, particularly in hard-to-understand areas
• [x] Tests added that prove fix is effective or that feature works

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.29%. Comparing base (84a43cc) to head (2decab8). Report is 8 commits behind head on develop.

Files	Patch %	Lines
pyrealm/pmodel/pmodel.py	88.88%	1 Missing :warning:
pyrealm/pmodel/subdaily.py	93.75%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #263 +/- ## ======================================== Coverage 95.29% 95.29% ======================================== Files 28 28 Lines 1720 1720 ======================================== Hits 1639 1639 Misses 81 81 ```

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[davidorme]

Do we need to add a bit more documentation to guide users on how they can use this new feature? Or is it in line with what we currently have?

Great point - I've added a short paragraph to the user facing PModel docs.