fix(ci): resolve uat lint + typecheck failures (CAR-1340)

- cache.py:38: Add explicit type annotation for redis.get() return value to resolve mypy no-any-return
- rate_limit.py: Remove duplicate forward-declaration block (dead code, mypy no-redef)
- conftest.py: Remove one excess blank line to satisfy ruff format check

All three fixes verified locally: ruff check ✅, ruff format ✅, mypy ✅

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cartsnitch_api/cache.py

@@ -35,7 +35,7 @@ class CacheClient:
     async def get(self, key: str) -> str | None:
         if not self._client:
             return None
-        value = await self._client.get(key)
+        value: str | bytes | None = await self._client.get(key)
         if value is None:
             return None
         if isinstance(value, bytes):