feat(redis): refactor Redis configuration to use multiple logical databases

- Updated default REDIS_URL to remove explicit /0 suffix
- Added dedicated Redis clients:
  - db0: general cache (redis_client)
  - db1: message cache (redis_message_client)
  - db2: binary storage (redis_binary_client)
  - db3: rate limiting (redis_rate_limit_client)
- Updated configuration, Docker files, and main startup lifecycle accordingly
- Replaced `get_redis()` usage in notification server with `redis_message_client`

docker-compose-osurx.yml

@@ -11,7 +11,7 @@ services:
     environment:
       - MYSQL_HOST=mysql
       - MYSQL_PORT=3306
-      - REDIS_URL=redis://redis:6379/0
+      - REDIS_URL=redis://redis:6379
       - ENABLE_OSU_RX=true
       - ENABLE_OSU_AP=true
       - ENABLE_ALL_MODS_PP=true