fix: support static files on pyodide / py.cafe under a prefix

[maartenbreddels]

When a shiny app is running under a prefix (root_path in ASGI terms), the static files are not served correctly under pyodide. This is because the ASGI path includes the root_path, and the root_path should be removed.
Starlette 0.33 and 0.34 however, did not set root_path correctly, and in those cases, we have to rely on route_path.

Related discussions:
encode/starlette#2400
encode/starlette#2361

A related fix we had in Solara:
widgetti/solara#413

But this fix also did not seem to work for our situation at https://py.cafe

I logged the output of the relevant entries in the scope dict, together with the starlette version:

starlette 0.32.0 {'path': '/strftime-min.js', 'root_path': '/_app/lib/strftime-0.9.2'}
starlette 0.33.0 {'path': '/_app/lib/strftime-0.9.2/strftime-min.js', 'root_path': '', 'route_root_path': '/lib/strftime-0.9.2', 'route_path': '/strftime-min.js'}
starlette 0.34.0 {'path': '/_app/lib/strftime-0.9.2/strftime-min.js', 'root_path': '', 'route_root_path': '/lib/strftime-0.9.2', 'route_path': '/strftime-min.js'}
starlette 0.35.0 {'path': '/_app/lib/strftime-0.9.2/strftime-min.js', 'root_path': '/_app/lib/strftime-0.9.2'}
starlette 0.36.0 {'path': '/_app/lib/strftime-0.9.2/strftime-min.js', 'root_path': '/_app/lib/strftime-0.9.2'}
starlette 0.37.2 {'path': '/_app/lib/strftime-0.9.2/strftime-min.js', 'root_path': '/_app/lib/strftime-0.9.2'}

This was using a similar situation as on py.cafe:

....
routes = [
    Mount('/static', app=app_static),
    Mount('/_app', app=app_shiny)
]

app = Starlette(routes=routes)

Which led me to the following fix, making shiny work under pyodide in combination with a prefix with the above mentioned versions of starlette.

[wch]

Thanks for the PR!

I had previously tried updating the version of starlette included with shinylive but that caused shiny to break, and this change appears to fix that issue.