Add coarse root history vars

[JessicaNeedham]

Description:

For WIEMIP (and maybe other projects) we need to output carbon in roots and carbon flux from roots to litter. In FATES we don't output coarse root carbon or coarse root carbon turnover. Since aboveground biomass fraction can vary by PFT, the only way to post-process these variables from sapwood and structural history variables is to output everything on PFT dimensions which is expensive. This PR adds these variables as FATES history variables.

Collaborators:

@rosiealice

Expectation of Answer Changes:

Not answer changing

Description of generative AI usage (as necessary)

No AI used

Checklist

If this is your first time contributing, please read the CONTRIBUTING document.

All checklist items must be checked to enable merging this pull request:

Contributor

• The in-code documentation has been updated with descriptive comments
• The documentation has been assessed to determine if updates are necessary
• Describe use of generative AI (if necessary)

Integrator

• FATES PASS/FAIL regression tests were run
• Evaluation of test results for answer changes was performed and results provided
• FATES-CLM6 Code Freeze: satellite phenology regression tests are b4b

If satellite phenology regressions are not b4b, please hold merge and notify the FATES development team.

Documentation

• Technical Note update:
• User's Guide update:

Test Results:

Running a short 5 year test to look at outputs now.
Here's croot:

And sapwood and structural carbon for comparison (different scales). Croot should be around 0.4 - 0.2 x the sum of these.