Port redis pubsub tests to fred

[rukai]

In order to update the redis dependency used by our test suite we will need to migrate the pubsub tests to use a different redis client.
This is because the new redis crate changed its pubsub support to disallow converting a connection between a pubsub connection and a regular connection.
This is a very reasonable position for them to take since the redis pubsub protocol is very silly and this lets them sidestep a bunch of its silliness.

However its a bit annoying for us since we need to test the cornercases of this silliness.

From a quick look at fred it looks like they do support pubsub/nonpubsub on the same connection:
https://docs.rs/fred/latest/fred/clients/struct.RedisClient.html#method.message_rx
https://docs.rs/fred/latest/fred/clients/struct.RedisClient.html#method.subscribe

We should be able to maintain some of our existing pubsub tests with redis crate and then add extra tests with fred.

If fred doesnt work out we should consider writing a super minimal client on top of redis-protocol, shouldnt be too bad.