Lint fixes, add .env.example, fix fp8_scaled_mm import path

- Remove unused imports (typing.Optional in config.py, uuid in models.py)
- Fix fp8_scaled_mm to use build_policy(checkpoint_path)
- Add .env.example with all configuration options

app/models.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import uuid
 from typing import Optional
 
 from pydantic import BaseModel, Field