Rothc: Soil file support + read options from settings file

[infotroph]

Description

• Reads texture, bulk density, soil C from a soil_physics file (currently with no fallback)
  • TODO let carbon values from IC override these
• Reads hydrology options and soil depth from settings$model, with fallback to RothC 2.1's out-of-the-box defaults.

Both were using constants hardcoded in write.config.RothC until now.

New utils function

Also adds PEcAn.utils::netcdf2df(), intended to be a general-purpose "please just dump this netcdf into a dataframe" function. So far I've tested it on files with only one dimension that varies (e.g. site-level files that might have a constant lat/lon alongside the depth or time); I'd love if it worked for higher dimensions too but did not tackle that today.

I use it here to read soil files -- I know PEcAn.data.land::pool_ic_netcdf2list() would work for this, but I'd rather not pull all the data.land dependencies into a model package if I don't have to.

Opinions requested on whether this is an improvement and where else it might come in handy.

Motivation and Context

Review Time Estimate

• Immediately
• Within one week
• When possible

Types of changes

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

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[infotroph]

Current test failure is for not declaring a data.land import (for pool_ic_netcdf2list), but on consideration that's avoidable. I'll refactor Now refactored.

[abbylewis]

@infotroph this all seems very reasonable to me. I added two very minor suggestions.