Add modf() in math.py

Author: namannimmo10

src/runtime/math.py

@@ -7,7 +7,13 @@
 
 # TODO: Change floor used inside functions implemented here to
 # floordiv operator (//) once the multiple import issue is fixed
-@overload
+
+def modf(x: f64) -> tuple[f64, i32]:
+    """
+    Return fractional and integral parts of `x` as a pair.
+    """
+    return (x - int(x), int(x))
+
 def factorial(x: i32) -> i32:
     """
     Computes the factorial of `x`.