Investigate adding another backend

[catanzaromj]

The last release of PHAT on pypi was v1.5 in 2017. Although it appears v1.7 was released in 2024, this release hasn't made it to pypi yet, which makes relying on it difficult for users of cechmate (i.e. it requires manual installation of dependencies).

I think we should move PHAT over to an optional dependency, as well as investigate adding another backend, like gudhi or dionysus. We should verify that any Rips-style constructors are valid with ripser.py, since that has been updated recently as well.