use camino::Utf8PathBuf in Path

[drernie]

This sounds like it would streamline our UPath code. I intend to use it for all our CLIs.

https://github.com/camino-rs/camino

[drernie]

Might simplify serialization:

serde1 adds serde Serialize and Deserialize impls for Utf8PathBuf and Utf8Path (zero-copy).