support for more scalar types

at the moment you can only really use `f64` as a scalar type, even though the scalar type `T` is a generic parameter everywhere.

- [x] `f32`, this should be easy to add, but would require https://github.com/martinjrobins/diffsl/issues/32 for diffsl
- [ ] `c32` / `c64`, there will be some modifications required to support this, not sure to what extent