Use `wasi-virt`-based VFS to store Python code

Currently, `componentize-py` "cheats" by assuming all required Python code will be loaded during the component pre-init step, and thus CPython won't need access to any of those files at runtime. This works surprisingly well, but will certainly break for more dynamic apps.

We should probably build a VFS by default, but also offer an option to use the "cheat" if desired.

Start by tracing how componentize-py currently loads Python code during component pre-init and review the proposed wasi-virt-based VFS approach. The work is done when a VFS is used by default for runtime file access while an option still enables the existing pre-init-only behavior, including support for more dynamic applications.

Written by the indexing model from the issue text.