Suggest implementing rand::Rand trait

This could look for types that have a constructor taking only a type implementing rand::Rng (from the rand crate) as an argument:

extern crate rand;
use rand::Rng;

struct Foo(u64);

impl Foo {
    fn new_random<R: Rng>(rng: &mut R) -> Self {
        Foo(rng.gen::<u64>())
    }
}

should become:

impl Rand for Foo {
    fn rand<R: Rng>(rng: &mut R) -> Self {
        Foo(rng.gen::<u64>())
    }
}

No files, tests, or entry points are named. Start by locating Clippy's lint registration and existing lints that inspect constructors or trait bounds, then check how lint tests are organized. Done means detecting the described rand::Rng constructor pattern and validating the suggested rand::Rand implementation through tests.