refactor: replace repeat().take() with repeat_n() for better performance

Replace `std::iter::repeat().take()` patterns with `std::iter::repeat_n()` in format_modifiers.rs. This change improves performance by avoiding the overhead of the `take()` iterator adapter and directly creating an iterator that yields the exact number of elements needed.

Author: mattsu2020

src/uu/date/src/format_modifiers.rs

@@ -401,7 +401,7 @@ fn apply_modifiers(
                 .try_reserve(target_len)
                 .map_err(|_| width_too_large_error())?;
             padded.push(sign);
-            padded.extend(std::iter::repeat('0').take(padding));
+            padded.extend(std::iter::repeat_n('0', padding));
             padded.push_str(rest);
             result = padded;
         } else {
@@ -414,7 +414,7 @@ fn apply_modifiers(
             padded
                 .try_reserve(target_len)
                 .map_err(|_| width_too_large_error())?;
-            padded.extend(std::iter::repeat(pad_char).take(padding));
+            padded.extend(std::iter::repeat_n(pad_char, padding));
             padded.push_str(&result);
             result = padded;
         }