✨ Add RedisPydanticStream backend

[random-things]

Provides a new backend--RedisPydanticStreamBackend--derived from RedisStreamBackend. Instead of a message: str being passed to publish, it takes a Pydantic BaseModel. On the other side, it deserializes the object back into a Pydantic model. Now that I'm reviewing this, I think it'd be beneficial to add the following to publish:

    async def publish(self: typing.Self, channel: str, message: BaseModel) -> None:
        """Publish a message to a channel."""
        msg_type: str = message.__class__.__name__
+
+        if msg_type not in self._module_cache:
+            self._module_cache[msg_type] = message.__class__
+
        message_json: str = message.model_dump_json()
        await self._producer.xadd(channel, {"msg_type": msg_type, "message": message_json})

But it would only be useful in rare cases (dynamically created models or models at lower-than-module scope) or specifically in the test case, dropping the import and class declaration into the test itself.

[alex-oleshkevich]

We do not accept any new backends. Please make it as a gist or separate package and link it in the readme.
#118