Add GemmType trait for dispatching gemm fn calls

[ivarflakstad]

I was wondering if this change would be of interest.
Removes the if-else-panic and let's the type system take care of that constraint instead.

[sarah-quinones]

thanks for the PR! though im not really sure if i want this. having no bounds is useful for usage in generic libraries, which is where the library is meant to be used. i'd prefer to leave it up to the consumers of the library to implement such a wrapper

[ivarflakstad]

Hmm I see, that's a valid point.
Still I want to emphasize that it is the exact same "bounds" as were there originally - except it was expressed through if statements.

So the only change I can see is that it will fail to build rather than panic at runtime.