fix: add more opaque black boxes in the tests

Author: art049

crates/criterion_compat/benches/criterion_integration/compare_functions.rs

@@ -1,4 +1,4 @@
-use codspeed_criterion_compat::{criterion_group, BenchmarkId, Criterion};
+use codspeed_criterion_compat::{black_box, criterion_group, BenchmarkId, Criterion};
 
 fn fibonacci_slow(n: u64) -> u64 {
     match n {
@@ -27,14 +27,16 @@ fn fibonacci_fast(n: u64) -> u64 {
 fn compare_fibonaccis(c: &mut Criterion) {
     let mut group = c.benchmark_group("Fibonacci");
 
-    group.bench_with_input("Recursive", &20, |b, i| b.iter(|| fibonacci_slow(*i)));
+    group.bench_with_input("Recursive", &20, |b, i| {
+        b.iter(|| fibonacci_slow(black_box(*i)))
+    });
     group.bench_with_input("Iterative", &20, |b, i| b.iter(|| fibonacci_fast(*i)));
 }
 fn compare_fibonaccis_group(c: &mut Criterion) {
     let mut group = c.benchmark_group("Fibonacci3");
     for i in 20..=21 {
         group.bench_with_input(BenchmarkId::new("Recursive", i), &i, |b, i| {
-            b.iter(|| fibonacci_slow(*i))
+            b.iter(|| fibonacci_slow(black_box(*i)))
         });
         group.bench_with_input(BenchmarkId::new("Iterative", i), &i, |b, i| {
             b.iter(|| fibonacci_fast(*i))