feat: Add FastAPI s6 sidecar PoC

- Sidecar DragonflyDB as Redis replacement
- Run pytheus in multiprocessing mode with Redis backend

requirements.txt

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+annotated-types==0.5.0
+anyio==3.7.1
+black==23.7.0
+click==8.1.6
+fastapi==0.101.0
+flake8==6.1.0
+gunicorn==21.2.0
+h11==0.14.0
+httptools==0.6.0
+idna==3.4
+mccabe==0.7.0
+mypy-extensions==1.0.0
+packaging==23.1
+pathspec==0.11.2
+platformdirs==3.10.0
+pycodestyle==2.11.0
+pydantic==2.1.1
+pydantic_core==2.4.0
+pyflakes==3.1.0
+pytheus==0.2.0
+python-dotenv==1.0.0
+PyYAML==6.0.1
+redis==4.6.0
+sniffio==1.3.0
+starlette==0.27.0
+typing_extensions==4.7.1
+uvicorn==0.23.2
+uvloop==0.17.0
+watchfiles==0.19.0
+websockets==11.0.3