Custom sensitivities for strided matmul never hit and I think are wrong

[oxinabox]

This file:
https://github.com/invenia/Nabla.jl/blob/4cadc87677fb1187354999dcf93bd528f45f85d0/src/sensitivities/linalg/strided.jl

it says:

const RS = StridedMatrix{<:∇Scalar}
const RST = Transpose{<:∇Scalar, RS}
const RSA = Adjoint{<:∇Scalar, RS}

But should say

const RS = StridedMatrix{<:∇Scalar}
const RST = Transpose{<:∇Scalar, <:RS}
const RSA = Adjoint{<:∇Scalar, <:RS}

Because otherwise RST are targetting Transpose{<:∇Scalar, Union(DenseArray, ...} (Similar for RSA).
Which will never occur in real code without manually costructing the Transpose

So ithink the only strided rules that are hit is:
(RS, RS, 'N', 'C', :Ȳ, :B, 'C', 'N', :A, :Ȳ)

And i think the others are wrong also, because i get errors that say GEMM is being used wrong when i change them to be that.

[oxinabox]

will be closed by #189