Create a Falcon demonstration in Pyodide

[vytas7]

Although installing a web framework in the browser is really a pointless and futile exercise, we could maybe still create a demo showcasing the test client? 🤔

In any case, I tried installing Falcon in Pyodide REPL just for fun, and hit quite many roadblocks.

• micropip picks only Falcon 2.0, because in the 3.x series we have no universal wheel. This will be addressed as part of the 4.0 release, where we ship one. I could specify the 4.0dev2 wheel by URL from TestPyPI.
• WSGI test client fails wsgiref validation: AssertionError: wsgi.errors (<pyodide.console._WriteStream object at 0x15653e8>) doesn't have the attribute writelines. Not sure if it is something we should address, or we could file a bug upstream. ⬅️ Filed as sys.stderr has no attribute writelines pyodide/pyodide#5053 for now.
• ASGI test client fails running anything, because our async_to_sync(...) doesn't work from inside a loop: RuntimeError: Runner.run() cannot be called from a running event loop. The Pyodide REPL seems to run the equivalent of python -m asyncio. ⬅️ Filed as falcon.async_to_sync() does not work inside an async loop #2321.

ASGIConductor works out of the box though!

(With Cibuildwheel, we could also prepare a binary Pyodide wheel for 3.13, but I think optimizing performance in this scenario is pretty much moot.)

One could take a look if it is easy to embed that REPL script with our code snippets preseeded, ideally with a selector to test different examples and/or tutorials.