Initialise casaflux%frac_sapwood=1 for use in casa_rplant (#373)

[rml599gh]

CABLE

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Description

casaflux%frac_sapwood needs to be initialised to 1 for the correct calculation of casaflux%crmplant(:,wood) in casa_rplant when cable_user%CALL_climate is not true.
This had been done in casa_inout at #274 but this subroutine is only used for offline simulations.
This change does the initialisation, in casa_init_pk, for ESM1.5/ESM1.6 cases.

Fixes #373

Type of change

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• [X ] Bug fix

Checklist

• The new content is accessible and located in the appropriate section.
• I have checked that links are valid and point to the intended content.
• I have checked my code/text and corrected any misspellings

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📚 Documentation preview 📚: https://cable--374.org.readthedocs.build/en/374/

[rml599gh]

Plots are January plant respiration (first month of a PIcontrol run). Note range on colour bar.

With frac_sapwood=1 initialisation (test done in copy of code from branch 368-merge-cablegithub-with-esm15-cable-for-esm16 in order to build with UM).

Without frac_sapwood iniatilisation in casa_init_pk (code copied from CABLE github branch 368-merge-cablegithub-with-esm15-cable-for-esm16

ACCESS-ESM1.5 executable

[ccarouge]

All good. Sorry for the delay.