switch the helper StackObj to a dataclass

Signed-off-by: Marshall Miller <[email protected]>

setools/policyrep/constraint.pxi

@@ -198,10 +198,10 @@ cdef class ConstraintExpression(PolicyObject):
             # lower precedence.
             stack = []
 
+            @dataclasses.dataclass(repr=False, eq=False, frozen=True)
             class StackObj:
-                def __init__(self, precedence, expression):
-                    self.precedence = precedence
-                    self.expression = expression
+                precedence: int
+                expression: List[str]
 
             for op in self._postfix:
                 if isinstance(op, frozenset) or op in _operands: