Bugfix/loss of precision when parsing value with unit (#15606)

Closes #12858

# Description
As explained in the ticket, easy to reproduce. Example: 1.07 minute is
1.07*60=64.2 secondes
```nushell
# before - wrong
> 1.07min
1min 4sec

# now - right
> 1.07min
1min 4sec 200ms
```

# User-Facing Changes
Bug is fixed when using ``into duration``.

# Tests + Formatting
Added a test for ``into duration``
Fixed ``parse_long_duration`` test: we gained precision 😄 

# After Submitting
Release notes? Or blog is enough? Let me know

crates/nu-command/tests/commands/into_duration.rs

@@ -0,0 +1,10 @@
+use nu_test_support::nu;
+
+// Tests happy paths
+
+#[test]
+fn into_duration_float() {
+    let actual = nu!(r#"1.07min | into duration"#);
+
+    assert_eq!("1min 4sec 200ms", actual.out);
+}

crates/nu-command/tests/commands/math/mod.rs

@@ -375,7 +375,7 @@ fn duration_decimal_math_with_nanoseconds() {
         "#
     ));
 
-    assert_eq!(actual.out, "1wk 3day 10ns");
+    assert_eq!(actual.out, "1wk 3day 12hr 10ns");
 }
 
 #[test]

crates/nu-command/tests/commands/mod.rs

@@ -54,6 +54,7 @@ mod insert;
 mod inspect;
 mod interleave;
 mod into_datetime;
+mod into_duration;
 mod into_filesize;
 mod into_int;
 mod join;