Declare [tf] Group as an "extra" for compatibility with pip

[IamJeffG]

Currently, the dependencies under [tool.poetry.group.tf.dependencies] in pyproject.toml are not recognized as pip extras. This makes it difficult to get dependencies tensorflow and tensorflow-hub via pip when using perch_hoplite.

Could you update the pyproject.toml to declare "tf" as an extra? I think this would go in the [project.optional-dependencies] section.

This would enable users to get perch_hoplite's transitive dependencies when we install the package like so:

pip install "perch_hoplite[tf] @ git+https://github.com/google-research/perch-hoplite.git"

[sdenton4]

Hey, Jeff!

I have given this a shot, but I'm getting strange behavior. Here's the PR:
#20

The optional dependency seems to work fine with a local copy, but the expected syntax with installing from github seems not to find the tf optional dependency:
https://github.com/google-research/perch-hoplite/actions/runs/13190083861/job/36821133718