Modules for Shiny Express

[jcheng5]

Example:

app.py

from counter import counter

from shiny.express import ui

counter("one")
ui.hr()
counter("two")

counter.py

from shiny import reactive
from shiny.express import module, render, ui


@module
def counter(input, output, session, starting_value=0):
    count = reactive.value(starting_value)

    ui.input_action_button("btn", "Increment")

    with ui.div():

        @render.express
        def current_count():
            count()

    @reactive.effect
    @reactive.event(input.btn)
    def increment():
        count.set(count() + 1)

[wch]

Note that there is a type-checking error, but it seems to be new to pyright 1.1.359 and is unrelated to the changes in this PR.