Catastrophically slow kernel in wfact!

[charleskawczynski]

Found in the nsight report for the aquaplanet dyamond on the latest main build. This corresponds to the two largest stencils mentioned here

The kernel looks like this on the atmos side:

precip_info =
    ((@name(c.ρq_rai), @name(ᶜwᵣ)), (@name(c.ρq_sno), @name(ᶜwₛ)))
MatrixFields.unrolled_foreach(precip_info) do (ρqₚ_name, wₚ_name)
    MatrixFields.has_field(Y, ρqₚ_name) || return

    ∂ᶜρqₚ_err_∂ᶜρqₚ = matrix[ρqₚ_name, ρqₚ_name]
    ᶜwₚ = MatrixFields.get_field(p, wₚ_name)
    ᶠtmp = p.ᶠtemp_CT3
    @. ᶠtmp = CT3(unit_basis_vector_data(CT3, ᶠlg)) * ᶠwinterp(ᶜJ, ᶜρ)

    # very slow
    @. ∂ᶜρqₚ_err_∂ᶜρqₚ +=
        dtγ * -(ᶜprecipdivᵥ_matrix()) ⋅ DiagonalMatrixRow(ᶠtmp) ⋅
        ᶠright_bias_matrix() ⋅ DiagonalMatrixRow(-(ᶜwₚ) / ᶜρ)
end

We should probably make a reproducer in ClimaCore and figure out why this is so slow.