Remove unwraps from non-test code in queue/redis

[svix-dylan]

We had a lot of unwraps in our Redis-based queue implementation. This PR refactors them to be .expect()s where appropriate, or to bubble errors up to a calling function that catches them.

[svix-dylan]

Would love feedback on this. I've only done a cursory run through. Open questions include, in functions that call and catch errors from the migrate_ functions -- how do we want to handle these errors? Currently I'm just passing them to a trace::error!. But they are nonrecoverable, right?

[tasn]

This was now fixed by @svix-james in another PR, no?