Make Bark a HF Pre-Trained Model

[sanchit-gandhi]

PR to make the Bark model a HF PreTrainedModel. The PreTrainedModel class takes care of all loading / saving logic, enabling checkpoints to be downloaded / pushed directly to the HF Hub:

from bark import GPT

model = GPT.from_pretrained("suno/bark-text")  # load model weights from Hub

Model weights on the HF Hub have version control and download counters. Users can also filter HF Hub models by type, e.g. by TTS.

Preliminarily, this PR only makes the required modelling code changes. The next step of the PR is to update generation.py, namely replacing the _load_model functionality with a single .from_pretrained call: https://github.com/suno-ai/bark/blob/d621ee3088f29f6d12c2d8b0503e2368f18fabd9/bark/generation.py#L169

Since Transformers is already a dependency of Bark, this adds no new dependency requirements. It also has no effect on the .forward call (functionality remains 1-to-1 the same).

For details on the PreTrainedModel class, refer to the code and docs.