Do not parenthesize nullary applications

Author: tothtamas28

pyk/src/pyk/klean/k2lean4.py

@@ -374,6 +374,9 @@ def _transform_arg(self, pattern: Pattern, *, concrete: bool = False) -> Term:
         if not isinstance(pattern, App):
             return term
 
+        if not pattern.args:
+            return term
+
         if pattern.symbol in self.structure_symbols:
             return term