## Summary
PEP 420 says [nested namespace
packages](https://peps.python.org/pep-0420/#nested-namespace-packages)
are allowed, i.e. marking a directory as a namespace package marks all
subdirectories in the subtree as namespace packages.
`is_package` is modified to use `Path::starts_with` and the order of
checks is reversed to do in-memory checks first before hitting the disk.
## Test Plan
Added unit tests. Previously all tests were run with `namespace_packages
== &[]`. Verified that one of the tests was failing before changing the
implementation.
## Future Improvements
The `is_package_with_cache` can probably be rewritten to avoid repeated
calls to `Path::starts_with`, by caching all directories up to the
`namespace_root`:
```ruff
let namespace_root = namespace_packages
.iter()
.filter(|namespace_package| path.starts_with(namespace_package))
.min();
```
Alexey Preobrazhenskiy
Charlie Marsh