Migrate to std black_box (#303)

Author: dani-garcia

crates/bitwarden-crypto/benches/default_allocator.rs

@@ -1,6 +1,8 @@
 #![allow(missing_docs)]
 
-use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use std::hint::black_box;
+
+use criterion::{criterion_group, criterion_main, Criterion};
 
 fn allocate_string(s: &str) -> String {
     s.to_owned()