Fixes missassignment of n_faces and n_nodes in fesom_to_ugrid

[wyatt-fluidnumerics]

Description

Previously, there was a bug in fesom_to_ugrid which mismatched the assignment of n_node and n_face. This PR resolves this issue thereby fixing downstream IndexSearch errors that occur during interpolation.

Checklist

• Closes Bug in assignment of faces vs nodes in fesom_to_ugrid() #2809
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
  • Describe how you used it (e.g., by pasting your prompt): This bug was originally found by claude while working on a local copy of the parcels-benchmarks repo. I then verified it and provided the fix myself.

[VeckoTheGecko]

Thanks for the PR @wyatt-fluidnumerics . I think that this looks good, but will leave it up to you or @fluidnumericsJoe for the final say.

Quick pulsecheck - do you have merge access already?

[wyatt-fluidnumerics]

Sounds good, I do have merge access already!

[erikvansebille]

Looks good to me!