Remove assumption of temperature

[CommonClimate]

In several places, the code assumes that users only want to reconstruct temperature, and that this variable is called 'tas' (e.g. in prep_graphem). This is an unnecessarily restrictive assumption, and may lead to bugs if people try to reconstruct any other field, or have other variable names.

Since cfr stands for "climate field reconstruction", I suggest calling the target variable "field" in graphem-related functions. It may also be good to check that the LMR part of the code does not assume too much either.

[fzhu2e]

Thanks. This issue is fixed in the latest version that has been merged into main.

Closing now. Please reopen if needed.

[fzhu2e]

OK, I realized that it's not just my code, but also the original code. Reopening...

[CommonClimate]

Yes, the original GraphEM code also assumes all climate fields are temperature. I will try to change that in my updates (see issue #4)