Class OptionalRng

poly-commit/src/optional_rng.rs:10–10

`OptionalRng` is a hack that is necessary because `Option<&mut R>` is not implicitly reborrowed like `&mut R` is. This causes problems when a variable of type `Option<&mut R>` is moved (eg, in a loop). To overcome this, we define the wrapper `OptionalRng` here that can be borrowed mutably, without fear of being moved.

/// To overcome this, we define the wrapper `OptionalRng` here that can be borrowed
/// mutably, without fear of being moved.
pub struct OptionalRng<R>(pub Option<R>);

impl<R: RngCore> RngCore for OptionalRng<R> {
    #[inline]