Relax Sized requirements on the rng

CHANGELOG.md

@@ -9,6 +9,9 @@ and this library adheres to Rust's notion of
 ### Changed
 - MSRV is now 1.63.0.
 - Migrated to `ff 0.14`, `rand_core 0.9`.
+- `group::Group::random(rng: impl RngCore) -> Self` has been changed to
+  `Group::random<R: RngCore + ?Sized>(rng: &mut R) -> Self`, to enable passing a
+  trait object as the RNG.
 
 ## [0.13.0] - 2022-12-06
 ### Changed

src/lib.rs

@@ -76,7 +76,7 @@ pub trait Group:
     /// this group.
     ///
     /// This function is non-deterministic, and samples from the user-provided RNG.
-    fn random(rng: impl RngCore) -> Self;
+    fn random<R: RngCore + ?Sized>(rng: &mut R) -> Self;
 
     /// Returns the additive identity, also known as the "neutral element".
     fn identity() -> Self;