Adopt standard Rust conventions for crate re-exports

This follows from an internal discussion.

From @bitwalker:

>IMO we should follow the normal Rust conventions for this stuff; you should re-export crates whose types you use in your public APIs, to avoid incompatible type errors downstream, but re-exporting the types themselves is not usually done.
>
>i.e. pub use miden_core; not pub use miden_core::{Felt, ...}