du: make -h the same precision as GNU coreutils

When printing the `du -h` output GNU coreutils does not print
fractions of the size, only the full number. E.g.:
```
truncate -s12M a
du -h --apparent-size a
12M	a
```
Align our version to do the same.

Closes: uutils#6159

src/uu/du/src/du.rs

@@ -555,7 +555,7 @@ impl StatPrinter {
                 for &(unit, power) in &UNITS {
                     let limit = multiplier.pow(power);
                     if size >= limit {
-                        return format!("{:.1}{}", (size as f64) / (limit as f64), unit);
+                        return format!("{:.0}{}", (size as f64) / (limit as f64), unit);
                     }
                 }
                 format!("{size}B")

tests/by-util/test_du.rs

@@ -543,6 +543,22 @@ fn test_du_h_flag_empty_file() {
         .stdout_only("0\tempty.txt\n");
 }
 
+#[test]
+fn test_du_h_precision() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    let fpath = at.plus("12M.txt");
+    std::fs::File::create(&fpath)
+        .expect("cannot create test file")
+        .set_len(12 * 1024 * 1024)
+        .expect("cannot truncate test len to size");
+    ucmd.arg("-h")
+        .arg("--apparent-size")
+        .arg(&fpath)
+        .succeeds()
+        .stdout_only(format!("12M\t{}\n", &fpath.to_string_lossy()));
+}
+
 #[cfg(feature = "touch")]
 #[test]
 fn test_du_time() {