matchers: use correct method for finding index in vector
The path matcher has an optimization for when all paths are `rootfilesin:`. This
optimization exists in both Python and Rust. However, the Rust implementation
currently has a bug that makes it fail in most cases. The bug is that it
`rfind()` where it was clearly intended to use `rposition()`. This patch fixes
that and adds a test.
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)