Fix direct use of rand in derive macro

[FSMaxB]

I currently get the error failed to resolve: use of undeclared crate or module rand when deriving fake::Dummy.

This is caused by using rand directly in the code that the derive macro generates.

To fix this, I added a #[doc(hidden)] reexport of rand to the fake crate.

In another commit, I also added a missing :: to a use of std.

If you want, I can also remove the pub use rand::Rng and replace all ::fake::Rng uses with ::fake::rand::Rng but I didn't do it for now just to make the most non-invasive change.

[FSMaxB]

Sorry, I always forget that RustRover doesn't turn rustfmt on by default.

I fixed the formatting and also added a commit to fix the clippy lints.

[francisdb]

Can we please get a release with this included?