`rand::RngCore` implementation for `numpy.random.Generator`

[flying-sheep]

We should allow a way to pass a numpy.random.Generator to a pyo3 function and use it on the Rust side by something requiring a rand::Rng by implementing rand::RngCore.

See

• https://numpy.org/doc/stable/reference/random/c-api.html
• https://numpy.org/doc/stable/reference/random/extending.html