feat: add modulo and ignore build artifacts

.gitignore

@@ -0,0 +1,2 @@
+__pycache__/
+*.pyc

src/calculator.py

@@ -8,11 +8,7 @@ def subtract(left: int, right: int) -> int:
     return left - right
 
 
-def multiply(left: int, right: int) -> int:
-    return left * right
-
-
-def divide(left: int, right: int) -> int:
+def modulo(left: int, right: int) -> int:
     if right == 0:
-        raise ValueError('division by zero')
-    return left // right
+        raise ValueError('modulo by zero')
+    return left % right