refactor(math): input validation

Input validation

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: BrianLusina

pymath/perfect_square/__init__.py

@@ -37,6 +37,11 @@ def num_squares(n: int) -> int:
     Returns:
         int: The least number of perfect square numbers that sum to n.
     """
+    if n < 0:
+        raise ValueError("n must be non-negative")
+    if n == 0:
+        return 0
+    
     dp = [float("inf")] * (n + 1)
     dp[0] = 0