Fix north/south buffer swap in CommunicationBuffers

[briochemc]

Remove Adapt.adapt_structure for CommunicationBuffers (unused since individual buffer types all adapt to nothing) and fix the south/north argument order in on_architecture to match the struct field order (west, east, south, north, ...), as per #5422 (comment).

Closes #5422

[glwagner]

nice find @briochemc

[simone-silvestri]

@briochemc the adapt is needed because the buffers are passed in the kernels in MultiRegion boundary conditions here

Oceananigans.jl/src/MultiRegion/multi_region_boundary_conditions.jl

Lines 37 to 45 in b8012d5

	function BoundaryConditions.fill_halo_regions!(c::MultiRegionObject, bcs, indices, loc, mrg::MultiRegionGrid, buffers, args...; fill_open_bcs=true, kwargs...)
	buff_ref = Reference(buffers.regional_objects)
	apply_regionally!(fill_send_buffers!, c, buffers, mrg)
	apply_regionally!(fill_halo_regions!, c, bcs, indices, loc, mrg, buff_ref, args...; fill_open_bcs, kwargs...)
	apply_regionally!(fill_send_buffers!, c, buffers, mrg)
	apply_regionally!(fill_halo_regions!, c, bcs, indices, loc, mrg, buff_ref, args...; fill_open_bcs, kwargs...)
	return nothing

However, these buffers are only passed for syntax convenience and thrown away inside GPU kernels. So if you find a clever way to detangle the buffers you can remove the adapt. It would require rewriting a custom fill_halo_regions!.

[briochemc]

OK so I have no clever ideas here so just reverting the method removal, and just keeping the swap fix.

[briochemc]

@simone-silvestri @glwagner Are you happy to merge this? I could run the CI and wait for it to pass but I don't think that's needed here 🤷 (I can't merge without CI passing)