Update catalan_numbers.rs with complexity analysis.

Author: AliAlimohammadi

src/dynamic_programming/catalan_numbers.rs

@@ -27,6 +27,12 @@
 ///
 /// A vector containing Catalan numbers from C(0) to C(upper_limit)
 ///
+/// # Complexity
+/// * Time complexity: O(n²)
+/// * Space complexity: O(n)
+///
+/// where `n` is the `upper_limit`.
+///
 /// # Examples
 ///
 /// ```