Add yac interface to couple to ICON

[nils3er]

This PR adds yac as a coupling library to FESOM, such that it can be coupled to ICON.

[nils3er]

@dsidoren @sveta-loza Can we sort out what needs to be done for merging this.
Especially the build system is a bit convoluted. Maybe @JanStreffing can help to streamline the changes with the existing coupling stuff?

[JanStreffing]

First, the checks are failing:
https://github.com/FESOM/fesom2/actions/runs/13158564989/job/36721281053?pr=683#step:6:915

 /__w/fesom2/fesom2/src/gen_forcing_couple.F90:276:9:

  276 |       end do
      |         1
Error: Expecting END SUBROUTINE statement at (1)

After that goes through I'll give this branch a try as coupled to openifs through oasis. Then someone also needs to test coupled to echam through oasis. @christian-stepanek maybe?

[JanStreffing]

I got around to testing this branch as part of AWI-CM3 (meaning oasis true, yac false). I get a compile time error:

/work/ab0246/a270092/model_codes/awicm3-v3.4/fesom-2.6/src/io_restart.F90:195:90:

  195 |   call ice_files%def_node_var_optional('ice_albedo', 'ice albedo',    '-',   ice%atmcoupl%ice_alb, mesh, partit)
      |                                                                                          1
Error: 'atmcoupl' at (1) is not a member of the 't_ice' structure

Full logfile attached.
comp.log

[JanStreffing]

Any update on this?
There seems to be interest in the community to use this interface.

[nils3er]

superseeded by #776