[ENG-3943]type check for event handler if spec arg are typed

[Lendemor]

bonus: fix arg spec of slider.on_change

following snippet will now raise error:

class SliderState(rx.State):
    value: int = 50

    def set_end(self, value: int): # should be `list[int]` to pass the typecheck
        self.value = value # should be `value[0]`

@rx.page
def index():
    return rx.vstack(
        rx.heading(SliderState.value),
        rx.slider(
            default_value=40,
            on_change=SliderState.set_end,
        ),
        width="100%",
    )

[adhami3310]

currently blocked on reflex-web to remove offending code

[Lendemor]

key is not used inside this particular method, should we remove the arg or did you mean to use it somewhere?

[linear]

ENG-3943 Slider on_change should return a single value, not a list

[adhami3310]

blocked on reflex-dev/reflex-web#1042