make ilist runtime resolve type

[kaihsin]

@dataclass
class IList(ir.Data[Sequence[T]], Sequence[T], Generic[T, L]):
    """A simple immutable list."""
    data:Sequence[T] 
    elem: types.TypeAttribute 

    def __init__(self, data:Sequence[T], elem: types.TypeAttribute | None = None):
           self.data = data
           if elem is None:
                self._infer_type()
           else:
                self.elem = elem
           self.type = types.Generic(IList, self.elem, types.Literal(len(self.data)))
          
    def _infer_type(self): ... #TODO