Decode cache data to the correct endpoint type

Use the return annotation to decode cached data to the correct type.
This follows the same logic FastAPI uses to JSON request bodies.

For the PickleCoder, this is a no-op as pickle already stores type
information in the serialised data.

fastapi_cache/decorator.py

@@ -10,6 +10,7 @@ else:
     from typing_extensions import ParamSpec
 
 from fastapi.concurrency import run_in_threadpool
+from fastapi.dependencies.utils import get_typed_return_annotation
 from starlette.requests import Request
 from starlette.responses import Response
 
@@ -79,6 +80,7 @@ def cache(
             (param for param in signature.parameters.values() if param.annotation is Response),
             None,
         )
+        return_type = get_typed_return_annotation(func)
 
         @wraps(func)
         async def inner(*args: P.args, **kwargs: P.kwargs) -> R:
@@ -139,7 +141,7 @@ def cache(
                 ttl, ret = 0, None
             if not request:
                 if ret is not None:
-                    return coder.decode(ret)
+                    return coder.decode_as_type(ret, type_=return_type)
                 ret = await ensure_async_func(*args, **kwargs)
                 try:
                     await backend.set(cache_key, coder.encode(ret), expire)
@@ -161,7 +163,7 @@ def cache(
                         response.status_code = 304
                         return response
                     response.headers["ETag"] = etag
-                return coder.decode(ret)
+                return coder.decode_as_type(ret, type_=return_type)
 
             ret = await ensure_async_func(*args, **kwargs)
             encoded_ret = coder.encode(ret)