Add a shareable generic datamode

[NickSzapiro-NOAA]

Description of changes

Adds a "generic" datamode to copy user-specified variables in streams for export

Specific notes

Started by adding just to datm, as that is the intended use in UFS

For the stream_variables to be available in InitializeAdvertise, refactored shr_strdata_init_from_config into advertise (stream config) and realize (on a mesh)

Contributors other than yourself, if any: Gemini AI

CDEPS Issues Fixed (include github issue #): #411

Are there dependencies on other component PRs (if so list): N/A

Are changes expected to change answers (bfb, different to roundoff, more substantial): bfb

Any User Interface Changes (namelist or namelist defaults changes): Adds a generic datamode, initially just to atm

Testing performed (e.g. aux_cdeps, CESM prealpha, etc): In progress. UFS regression tests pass

Hashes used for testing: TODO

[NickSzapiro-NOAA]

This seems to be working now. One test is that it is bit-for-bit in UFS instead of "GEFS" datm datamode tests, as no variables need to be calculated/diagnosed.

I'm not sure how to test in CESM setups.
Would you be interested in testing this is in your systems @billsacks @mvertens ? Generic should work for datm cplhist, if you simply change datm_in datamode=GENERIC instead

[billsacks]

Thank you for this contribution, @NickSzapiro-NOAA . I am overloaded right now so I'm not sure when I'll get a chance to review this myself.

Contributors other than yourself, if any: Gemini AI

Thank you for acknowledging the contribution of Gemini to this PR. To help determine our next steps here, can you please comment on how carefully you have reviewed and come to understand the Gemini-produced code yourself?

[NickSzapiro-NOAA]

Thanks for letting me know

I would say pair programming with Gemini AI on this ended up being more trouble than it was worth, subroutine hallucinations and all. The github CI was helpful though. I am responsible for these code changes

[billsacks]

I would say pair programming with Gemini AI on this ended up being more trouble than it was worth, subroutine hallucinations and all. The github CI was helpful though. I am responsible for these code changes

Okay, thanks – that's helpful to know!

I want to chat with @mvertens about this and then will get back to you.