[Bug]: errors that occur on bookmark don't generate a stacktrace

[cpsievert]

Currently, when you bookmark, you do get a notification of the error in the UI, but nothing is printed to the Python console (or logged).

from shiny.express import app_opts, session, ui

app_opts(bookmark_store="url")

ui.input_bookmark_button("Bookmark this")

ui.input_slider("slider", "Slider", 0, 100, 50)

@session.bookmark.on_bookmarked
async def _(url: str):
    raise Exception("boom!")