feat: effect_refreshable.on support async

[CrystalWindSnake]

import asyncio
from nicegui import ui
from ex4nicegui import rxui, effect_refreshable


@ui.page("/")
async def index():
    count = rxui.var(0)

    def plus_one():
        count.value += 1

    # ui
    ui.button(text="click me", on_click=plus_one)

    @effect_refreshable.on(count)
    async def _():
        await asyncio.sleep(0.5)
        ui.label(f"count: {int(count.value)}")