Implement Epistula

[bkb2135]

Changes

• Switch from Bittensor communication protocol to Epistula.
• Switch from vLLM to transformers architecture.
• Switch from async generators to OpenAI httpx clients for streaming.

Other

• Fix the whole codebase style/format/isort issues to align with ruff, black, isort.
• Add ruff, black, isort.
• Add pre-commit hook, pre-commit checks on pull-request with Github Actions.
• Add contribution guide to CONTRIBUTING.md.
• Remove Llama 8B model.

Overview

Each git commit will run pre-commit hook locally, and fix all format/style issues.
If commit fails, make sure to add the modified files.

To run pre-commit manually and automatically fix files:
poetry run pre-commit run --all-files

[dbobrenko]

LGTM, great stuff