Rust: Creation of QFunctions from C source

Hi,

In #1621, it was mentioned that functionality to create QFunctions from C source through the Rust bindings would be reasonably straightforward to implement. This would allow usage of the JIT backends when using the Rust bindings from what I can tell. (With this type of QFunction creation, is it still possible to run non-JIT on CPU?)

First, I would like to hear some general opinions on including this as a feature next to QFunctions from the gallery and QFunctions from closures.

Secondly, given that this probably not high on your priority list, I'm happy to contribute to this (with some guidance) if that would be welcome/helpful.