os.walk() is overkill and may bring wrong packages

Ni!
Using `os.walk()` in `get_locally_installed_packages()` will break in case a parent directory of multiple python versions slips by accident into `sys.path`. For example, if `sys.path` contains `"/usr/lib/"`, the walk will traverse all packages-like descendant directories, no matter if they're is in `sys.path` or not.

A solution would be to check whether something like `root[ len(path.rstrip(os.sep) + 1):].count(os.sep) == 1` to ensure we only look inside child directories, where python would actually look.

Locate get_locally_installed_packages() and inspect how os.walk() processes each sys.path entry. Reproduce the case with a parent directory such as /usr/lib/ in sys.path, then verify that only direct child package directories are considered rather than deeper descendants.

Written by the indexing model from the issue text.