Move approximate equality test for floats to util

tests/common/f64_utils.rs

@@ -0,0 +1,4 @@
+pub fn approx_equal(a: f64, b: f64, dp: u8) -> bool {
+    let p = 10f64.powi(-(dp as i32));
+    (a - b).abs() < p
+}

tests/common/mod.rs

@@ -1,4 +1,5 @@
 pub mod cli_arguments;
+pub mod f64_utils;
 pub mod file_util;
 pub mod hash_util;
 pub mod lexicographic_file_walker;