chtMultiRegionFoam looses heat due to explicit coupling

Functionality to add/problem to solve

chtMultiRegionFoam looses heat when evaluating 'mapped' type bcs (e.g. compressible::turbulentTemperatureRadCoupledMixed). This is because the owner side evaluates with 'old' neighbour side values but the neighbour side evaluates with the 'new' owner side values.

This should instead use a scheme where the owner side also updates the neighbour side patch.

Target audience

cht on closed domains. See e.g. https://develop.openfoam.com/Development/openfoam/-/blob/develop/applications/test/multiWorld/solidFoam/solid1_solid2 testcase.

Switch off the kappaLayers, switch to transient, switch on the debug flag for the BC so it prints the heat flux for both sides.