Precompute mismatch scaling factor

[briochemc]

Specifically, refactor these to allow the user to provide transpose(o) * W * o instead of recalculating it every time:

AIBECS.jl/src/multiTracer.jl

Lines 321 to 355 in 960ecad

	## new functions for more generic obs packages
	# TODO Add an optional function argument to transform the data before computingn the mismatch
	# Example if for isotope tracers X where one ususally wants to minimize the mismatch in δ or ε.
	function mismatch(x, grd::OceanGrid, obs; c=identity, W=I, M=interpolationmatrix(grd, obs.metadata), iwet=iswet(grd, obs))
	o = view(obs, iwet)
	δx = M * c(x) - o
	return 0.5 * transpose(δx) * W * δx / (transpose(o) * W * o)
	end
	mismatch(x, grd::OceanGrid, ::Missing; kwargs...) = 0
	function ∇mismatch(x, grd::OceanGrid, obs; c=identity, W=I, M=interpolationmatrix(grd, obs.metadata), iwet=iswet(grd, obs))
	∇c = Diagonal(ForwardDiff.derivative(λ -> c(x .+ λ), 0.0))
	o = view(obs, iwet)
	δx = M * c(x) - o
	return transpose(W * δx) * M * ∇c / (transpose(o) * W * o)
	end
	∇mismatch(x, grd::OceanGrid, ::Missing; kwargs...) = transpose(zeros(length(x)))
	# In case the mismatch is not based on the tracer but on some function of it
	function indirectmismatch(xs::Tuple, grd::OceanGrid, modify::Function, obs, i, M=interpolationmatrix(grd, obs[i].metadata), iwet=iswet(grd, obs[i]))
	x2 = modify(xs...)
	out = 0.0
	M = interpolationmatrix(grd, obs[i].metadata)
	iwet = iswet(grd, obs[i])
	o = view(obs[i], iwet)
	δx = M * x2[i] - o
	return 0.5 * transpose(δx) * δx / (transpose(o) * o)
	end
	function ∇indirectmismatch(xs::Tuple, grd::OceanGrid, modify::Function, obs, i, M=interpolationmatrix(grd, obs[i].metadata), iwet=iswet(grd, obs[i]))
	nt, nb = length(xs), length(iswet(grd))
	x2 = modify(xs...)
	o = view(obs[i], iwet)
	δx = M * x2[i] - o
	∇modᵢ = ∇modify(modify, xs, i)
	return transpose(δx) * M * ∇modᵢ / (transpose(o) * o)
	end