Add typing to binary_exponentiation.py (#9471)

* Add typing to binary_exponentiation.py

* Update binary_exponentiation.py

* float to int division change as per review

Author: saksham-chawla

Diff for: maths/binary_exponentiation.py

@@ -4,15 +4,15 @@
 # Time Complexity : O(logn)
 
 
-def binary_exponentiation(a, n):
+def binary_exponentiation(a: int, n: int) -> int:
     if n == 0:
         return 1
 
     elif n % 2 == 1:
         return binary_exponentiation(a, n - 1) * a
 
     else:
-        b = binary_exponentiation(a, n / 2)
+        b = binary_exponentiation(a, n // 2)
         return b * b