Fix v_args when used on classes with non-callable members

lark/visitors.py

@@ -74,6 +74,8 @@ class Transformer:
         for name, value in getmembers(cls):
             if name.startswith('_') or name in libmembers:
                 continue
+            if not callable(cls.__dict__[name]):
+                continue
 
             # Skip if v_args already applied (at the function level)
             if hasattr(cls.__dict__[name], 'vargs_applied'):

tests/test_trees.py

@@ -137,6 +137,8 @@ class TestTrees(TestCase):
             f = float
             sub = lambda self, a, b: a-b
 
+            not_a_method = {'other': 'stuff'}
+
             @v_args(inline=False)
             def add(self, values):
                 return sum(values)