Option to not cycle met drivers for CO2, plus multiple minor bug fixes

[mpaiao]

This PR allows cycling met drivers but using actual year CO2. It also fixes multiple minor bugs in the code.

Description

This change allows increasing CO2 whilst cycling meteorological drivers, which can be useful in factorial experiments. If CO2 is provided in a separate set of met drivers containing only CO2, the code will look for files from the actual simulation year as opposed to cycling the years. This will be activated only for CO2, and only if the files outside the main meteorological cycle are found. Otherwise, the code falls back to the default (i.e., cycling all the meteorological variables and CO2).

I also implemented a series of minor bug fixes / minor improvements:

1. Replaced a few case-like if statements with select case (safer for case selection).
2. Added some new output variables.
3. Fixed metadata units of some output variables.
4. Renamed a couple of variables and sub-routines that had misleading names (e.g. avg_monthly_pcpg is now avg_monthly_accp so it is clear that is accumulated precipitation, not precipitation rate).
5. Added some new error reports to make debugging easier.
6. Fixed seed dispersal error when non-local dispersal occurs across multiple sites (only affects runs with more than 1 site per polygon).

Collaborators

Motivation and Context

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

Testing :

• All new and existing tests passed.