Add MicroPython as ReactPy executor

[Archmonger]

Current Situation

Currently, our client-side components use pyodide to execute ReactPy. However, Pyodide unfortunately has a pretty slow boot-up time.

Proposed Actions

Try using MicroPython to render ReactPy instead. Because MicroPython does not support installing packages from PyPi, this may involve creating our own system for manually fetching wheels, storing them locally, and then serving them.

There are some instructions on MicroPython's docs on how to build compatible apps, and a bit more detail on the micropython-lib docs.

Rather than this feature being a completely separate executor, it's likely that we will build it into the the existing ReactPyCsr executor via an ReactPyCsr(interpreter = "micropython") flag.