Make backends store bytes instead of strings

This is, for the majority of backends, the native format anyway, and so
we save encoding and decoding when using the PickleCodec or if (in future)
a orjson Coder was to be added.

For the JsonCodec, the only thing that changed is the location where the
JSON data is encoded to bytes and decoded back again to a string.

fastapi_cache/coder.py

@@ -1,9 +1,8 @@
-import codecs
 import datetime
 import json
 import pickle  # nosec:B403
 from decimal import Decimal
-from typing import Any, Callable, ClassVar, Dict, TypeVar, overload
+from typing import Any, Callable, ClassVar, Dict, Optional, TypeVar, Union, overload
 
 import pendulum
 from fastapi.encoders import jsonable_encoder
@@ -46,11 +45,11 @@ def object_hook(obj: Any) -> Any:
 
 class Coder:
     @classmethod
-    def encode(cls, value: Any) -> str:
+    def encode(cls, value: Any) -> bytes:
         raise NotImplementedError
 
     @classmethod
-    def decode(cls, value: str) -> Any:
+    def decode(cls, value: bytes) -> Any:
         raise NotImplementedError
 
     # (Shared) cache for endpoint return types to Pydantic model fields.
@@ -62,16 +61,16 @@ class Coder:
 
     @overload
     @classmethod
-    def decode_as_type(cls, value: str, type_: _T) -> _T:
+    def decode_as_type(cls, value: bytes, *, type_: _T) -> _T:
         ...
 
     @overload
     @classmethod
-    def decode_as_type(cls, value: str, *, type_: None) -> Any:
+    def decode_as_type(cls, value: bytes, *, type_: None) -> Any:
         ...
 
     @classmethod
-    def decode_as_type(cls, value: str, *, type_: _T | None) -> _T | Any:
+    def decode_as_type(cls, value: bytes, *, type_: Optional[_T]) -> Union[_T, Any]:
         """Decode value to the specific given type
 
         The default implementation uses the Pydantic model system to convert the value.
@@ -95,29 +94,32 @@ class Coder:
 
 class JsonCoder(Coder):
     @classmethod
-    def encode(cls, value: Any) -> str:
+    def encode(cls, value: Any) -> bytes:
         if isinstance(value, JSONResponse):
-            return value.body.decode()
-        return json.dumps(value, cls=JsonEncoder)
+            return value.body
+        return json.dumps(value, cls=JsonEncoder).encode()
 
     @classmethod
-    def decode(cls, value: str) -> str:
-        return json.loads(value, object_hook=object_hook)
+    def decode(cls, value: bytes) -> Any:
+        # explicitly decode from UTF-8 bytes first, as otherwise
+        # json.loads() will first have to detect the correct UTF-
+        # encoding used.
+        return json.loads(value.decode(), object_hook=object_hook)
 
 
 class PickleCoder(Coder):
     @classmethod
-    def encode(cls, value: Any) -> str:
+    def encode(cls, value: Any) -> bytes:
         if isinstance(value, TemplateResponse):
             value = value.body
-        return codecs.encode(pickle.dumps(value), "base64").decode()
+        return pickle.dumps(value)
 
     @classmethod
-    def decode(cls, value: str) -> Any:
-        return pickle.loads(codecs.decode(value.encode(), "base64"))  # nosec:B403,B301
+    def decode(cls, value: bytes) -> Any:
+        return pickle.loads(value)  # nosec:B403,B301
 
     @classmethod
-    def decode_as_type(cls, value: str, *, type_: Any) -> Any:
+    def decode_as_type(cls, value: bytes, *, type_: Optional[_T]) -> Any:
         # Pickle already produces the correct type on decoding, no point
         # in paying an extra performance penalty for pydantic to discover
         # the same.