Flux coupling edits

[kieranricardo]

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• Short (1 sentence) summary of your PR:
  This introduces changes when running icepack in calc_tsfc=.false. mode for coupling with fluxes supplied from an atmosphere model.

• Developer(s):
  @kieranricardo @blimlim

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• How much do the PR code changes differ from the unmodified code?

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When calc_tsfc=.false. the conductive flux is now capped, and it is also reduced during temperature_changes if the thermo solve is struggling to converge. The excess flux is accounted for in the energy calculations.

Also, hs_min is made configurable. A larger value than the default is needed for numerical stability when run with calc_tsfc=.false..

[kieranricardo]

hey @anton-seaice, can you give this a look over before I make a PR into the CICE-consortium icepack? 👀

[anton-seaice]

I will look properly, but i think split this into two changes, one for hs_min and one for the cap_fluxes stuff