Cache modules not included in the Python Standard Library

[pdawyndt]

Loading pyodide for the first time takes some time, but the next time you use Papyros this goes much faster due to proper caching.

Loading an imported module (e.g. pylab) beyond the Python Standard Library for the first time (these modules seems to be included in the pyodide load) take some time, but is not cached. If Papyros is refreshed, these modules have to be reloaded. We could think about a proper cache strategy here as well.