refactor(test_pr.rs): reorganize imports for better readability

Reordered imports in test_pr.rs to group standard library imports together and move uutests imports to the bottom, improving code organization and readability.

Author: mattsu2020

tests/by-util/test_pr.rs

@@ -7,9 +7,9 @@
 use jiff::{Timestamp, ToSpan};
 use regex::Regex;
 use std::fs::metadata;
-use uutests::util::UCommand;
 #[cfg(unix)]
 use uutests::at_and_ts;
+use uutests::util::UCommand;
 use uutests::{at_and_ucmd, new_ucmd};
 
 const DATE_TIME_FORMAT_DEFAULT: &str = "%Y-%m-%d %H:%M";