Using pyrealm within the Plants model

[davidorme]

Description

This PR is to replace the placeholder internals of the Plants Model with actual pyrealm functionality. That is very hard to do in small steps, so this will be a large PR.

• Replaces old plants config with new setup for T model parameters
• Replaces flora structure with pyrealm Flora
• Replaces cohort structure with pyrealm Cohorts
• Replaces community structure with pyrealm Community
• Uses pyrealm demography functionality to go from cohort DBH data to allometry
• Uses PModel to estimate GPP and transpiration.

Fixes #659
Fixes #655

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