Cleanup of the mono-repo

This PR:

standardizes the metadata files (LICENSE, .gitignore, etc.) in each crate,
removes leftover files from when we switched to the mono-repo structure,
properly uses workspace dependencies instead of managing dependency versions in each member crate
removes the pyo3 dependency from crates/symagen in preparation for pypi/symagen
removes crates/py-clam in preparation for pypi/abd-clam

URI-ABD / clam