docs(zeroize): fix docstring warnings

Signed-off-by: Paul Spooren <mail@aparcar.org>

util/src/zeroize/zeroized_ext.rs

@@ -1,6 +1,8 @@
 use zeroize::Zeroize;
 
+/// Extension trait providing a method for zeroizing a value and returning it
 pub trait ZeroizedExt: Zeroize + Sized {
+    /// Zeroizes the value in place and returns self
     fn zeroized(mut self) -> Self {
         self.zeroize();
         self