simplify inversion algorithm to improve readability by using bitunils inversion method

src/divide.py

@@ -11,15 +11,9 @@ def divide(n, int_x, int_y, method):
         invert = False
         for i in x[::-1]:
             if invert:
-                if i == '0':
-                    x_inv += '1'
-                else:
-                    x_inv += '0'
+                x_inv += bu.inv(i)
             else:
-                if i == '0':
-                    x_inv += '0'
-                else:
-                    x_inv += '1'
+                x_inv += i
 
             if i == '1':
                 invert = True