Define type of init_val for reduction as Any

src/pystencils/backend/kernelcreation/freeze.py

@@ -195,6 +195,7 @@ class FreezeExpressions:
 
         # match for reduction operation and set neutral init_val and new rhs (similar to augmented assignment)
         new_rhs: PsExpression
+        init_val: Any  # TODO: type?
         match expr.op:
             case "+":
                 init_val = PsConstant(0)