Fix #137 - Allow the passthrough option for the cache

[WebReflection]

This MR goal is to fix #137 so that a passthrough value for the packages_cache entry in the config would allow direct Pyodide bootstrap without needing, or using, micropip.

This should basically guarantee the following:

• if no cache is meant/needed, passthrough would avoid the usage of micropip entirely
• all invalidation issues about the Pyodide version won't matter anymore, it's the current Pyodide bootstrapping without a lockFileURL detail

This should solve all concerns and allow power users to bypass our cache logic which is, apparently, not always desired.