feat: implement RedisCache backend for QueryResult caching

[Einswilli]

The documentation mentions a RedisCache backend, but currently only MemoryCache is implemented in ryx/cache.py.

Goal: Implement the RedisCache class by inheriting from AbstractCache. It should use the redis-py (async) library to store and retrieve cached query results.

Implementation hint:

1. Add redis as an optional dependency.
2. Implement get, set, delete, delete_many, clear, and keys in ryx/cache.py.
3. Ensure that values are serialized/deserialized (e.g., using json or pickle) since Redis stores strings/bytes.