Allow `At` to have a different type than `A`

[klamike]

#22 (comment)

[gdalle]

This is a two-sided sword though, because if we keep the naïve transpose(A) in general, it will lead to a CSC-vector product, which is much less GPU-friendly than CSR-vector

[klamike]

Good point... but we can just relax the type parameters while keeping the current eager conversion logic. Perhaps we can add a flag, something like lazy_transpose=true, to bypass the convert(typeof(A)? Then we can add a hint to the MethodError to try passing lazy_transpose=true to avoid the error, with a warning regarding performance.

[klamike]

Or we can have some wrapper over Base.transpose e.g. coolpdlp_allocate_transpose that users can override for their types..