gate the benchmark behind the bench feature that it uses (#8)

* gate the benchmark behind the bench feature that it uses, so that 'cargo bench --no-default-features' doesn't have compilation errors

* Change cfg(bench) to feature bench

* Fixup clippy

---------

Co-authored-by: MarcusGrass <marcus.grass@protonmail.com>

tiny-bench/benches/benchmark.rs

@@ -1,13 +1,20 @@
+#[cfg(feature = "bench")]
 use std::time::Duration;
+#[cfg(feature = "bench")]
 use tiny_bench::{black_box, BenchmarkConfig};
 
 fn main() {
+    #[cfg(feature = "bench")]
     bench_test_one();
+    #[cfg(feature = "bench")]
     bench_test_two();
+    #[cfg(feature = "bench")]
     bench_test_three();
+    #[cfg(feature = "bench")]
     bench_test_four();
 }
 
+#[cfg(feature = "bench")]
 fn bench_test_one() {
     tiny_bench::bench_labeled("test one", || {
         let mut v: Vec<i32> = Vec::with_capacity(10_000);
@@ -22,6 +29,7 @@ fn bench_test_one() {
     });
 }
 
+#[cfg(feature = "bench")]
 fn bench_test_two() {
     tiny_bench::bench_with_setup_labeled(
         "test two",
@@ -43,10 +51,12 @@ fn bench_test_two() {
     );
 }
 
+#[cfg(feature = "bench")]
 fn bench_test_three() {
     tiny_bench::bench_labeled("test three, empty", || {});
 }
 
+#[cfg(feature = "bench")]
 fn bench_test_four() {
     tiny_bench::bench_with_configuration_labeled(
         "test four, max_it",

tiny-bench/src/output/analysis/criterion/mod.rs

@@ -18,6 +18,7 @@ use std::time::Duration;
 /// }
 /// ```
 #[allow(unsafe_code)]
+#[allow(clippy::mem_forget)]
 pub fn black_box<T>(dummy: T) -> T {
     unsafe {
         let ret = std::ptr::read_volatile(&dummy);