benches: fix deprecation warnings for black_box

Fixes:
"warning: use of deprecated function `criterion::black_box`: use `std::hint::black_box()` instead"

Author: tmatth

benches/bench.rs

@@ -29,6 +29,7 @@ use crate::rdo::rdo;
 use crate::transform::{forward_transforms, inverse_transforms};
 
 use criterion::*;
+use std::hint::black_box;
 use std::sync::Arc;
 use std::time::Duration;
 

benches/dist.rs

@@ -21,6 +21,7 @@ use rav1e::bench::rdo::DistortionScale;
 use rav1e::bench::tiling::*;
 use rav1e::bench::util::Aligned;
 use rav1e::Pixel;
+use std::hint::black_box;
 
 const DIST_BENCH_SET: &[(BlockSize, usize)] = &[
   (BLOCK_4X4, 8),

benches/mc.rs

@@ -16,6 +16,7 @@ use rav1e::bench::partition::RefType;
 use rav1e::bench::util::Aligned;
 use rav1e::context::{BlockOffset, TileBlockOffset};
 use rav1e::prelude::*;
+use std::hint::black_box;
 use std::sync::Arc;
 
 fn bench_put_8tap_top_left_lbd(c: &mut Criterion) {