id: mark passwd-format and pretty-print as conflicting

These are non-sensical to combine, and didn't work reasonably anyway.
Also, passwd-formatting is our own extension, so there is no need for
compatibility anyway.

src/uu/id/src/id.rs

@@ -397,6 +397,7 @@ pub fn uu_app() -> Command {
             Arg::new(options::OPT_PASSWORD)
                 .short('P')
                 .help("Display the id as a password file entry.")
+                .conflicts_with(options::OPT_HUMAN_READABLE)
                 .action(ArgAction::SetTrue),
         )
         .arg(

tests/by-util/test_id.rs

@@ -461,3 +461,16 @@ fn test_id_no_specified_user_posixly() {
         }
     }
 }
+
+#[test]
+#[cfg(all(unix, not(target_os = "android")))]
+fn test_id_pretty_print_password_record() {
+    // `-p` is BSD only and not supported on GNU's `id`.
+    // `-P` is our own extension, and not supported by either GNU nor BSD.
+    // These must conflict, because they both set the output format.
+    new_ucmd!()
+        .arg("-p")
+        .arg("-P")
+        .fails()
+        .stderr_contains("the argument '-p' cannot be used with '-P'");
+}