Add last_digit function with type hints and doctests

Author: prachi757

maths/last_digit.py

@@ -0,0 +1,12 @@
+def last_digit(n: int) -> int:
+    """
+    Return the last digit of a given integer.
+
+    >>> last_digit(1234)
+    4
+    >>> last_digit(-98)
+    8
+    >>> last_digit(0)
+    0
+    """
+    return abs(n) % 10