ReactPy ASGI Middleware and standalone ReactPy ASGI App

[Archmonger]

Issues

• fix ReactPy ASGI App and Middleware #1110
• fix Modify SimpleReactPyClient to not use pre-defined endpoints #1079
• fix Improve Reconnecting WS Configurability #525
• fix Embedding ReactPy via Template Tags #653

Solution

Create a ReactPy ASGI application and middleware.

Features of the ASGI application/middleware

• Gain compatibility with every ASGI framework.
• Allows ReactPy to be "self contained" if needed (run within any ASGI webserver without a backend).

For example, this is the interface for ReactPy's standalone mode:

from reactpy import component, html
from reactpy.asgi.standalone import ReactPy

@component
def Example():
    return html.div("Hello World")

app = ReactPy(Example)
# Now you can run `uvicorn example:app --reload` to start ReactPy!

Major Changes

• ReactPy class has been created as the standalone API for ReactPy.
• ReactPyMiddleware has been created as the version of ReactPy that can wrap other ASGI web frameworks.
• Added a template tag to use alongside our middleware.
• @reactpy/client has been rewritten to be more modular. This also helps in preparation for template tags.
• reactpy.backends.* is removed.

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

_{By submitting this pull request I agree that all contributions comply with this project's open source license(s).}

[Archmonger]

The more I develop this, the more I realize it's unwise to finish this PR until the following issues are closed

• Modify SimpleReactPyClient to not use pre-defined endpoints #1079
• Embedding ReactPy via Template Tags #653

This PR is in a 90% finished state, but I will hold off on finishing it for now and refocus on template tags.

[Archmonger]

@rmorshea I will implement things using starlette for static files now, but ideally I don't want a web framework to be a dependency for us.

I would feel more comfortable using whitenoise as it's a static-file focused library that doesn't have extra stuff. However, this relies on this PR getting merged:

• FORKED: AsgiWhiteNoise and async WhiteNoiseMiddleware evansd/whitenoise#359

[Archmonger]

Note to self:
It seems logical to mandate that ReactPy standalone's root component must be a html.html node. By forcing the user to template the whole page, this would eliminate the need for a janky Options(head=...) parameter.

html.html(
    {"lang": "en"},
    html.head(
        ...,
    ),
    html.body(
        ...,
    ),
)

It also seems logical to have ReactPyStandalone and ReactPyMiddleware to be discrete classes.

EDIT: Not realistic since the root object needs to be a component, not VDOM.