Remove unsafe from new on RND

Unsafe is not required here given that all futures are required to live longer than their global peripheral instances. There are other occurrences of unsafe being used on new that should be removed. I started to do that but then went down a bit of a rabbit hole.

embassy-nrf/src/rng.rs

@@ -52,7 +52,7 @@ impl<'d> Rng<'d> {
     /// e.g. using `mem::forget`.
     ///
     /// The synchronous API is safe.
-    pub unsafe fn new(
+    pub fn new(
         _rng: impl Unborrow<Target = RNG> + 'd,
         irq: impl Unborrow<Target = interrupt::RNG> + 'd,
     ) -> Self {