when using mewnala after installing it can't find the "assets_directory"

this was anticipated since we only just now published a library.

All the ways we use assets atm:

1. we run a rust example that uses currently called libprocessing
2. we run a just command that will run a python sketch inside of crates/processing_pyo3/examples which automatically sets the asset path using PROCESSING_ASSET_PATH (see: justfile)
3. You activate the virtual env inside of crates/processing_pyo3 and run a python sketch in there
4. Someone has installed mewnala (pip install mewnala) and needs to run a sketch that looks at assets

4 is broken, 3 might be broken. We need to cover all 4 cases.