fix: MOVED was not being redirected

[rafaelclp]

Issue

When using iredis on a redis cluster, MOVED responses are not redirected.

After some debugging, I noticed iredis works when paired with redis==5, but not with redis==7.2:

Reason

Prior to redis-py 6, MOVED responses raised a ResponseError("MOVED <SLOT> <ADDR>"). When using redis.ClusterRedis, they raised MovedError("<SLOT> <ADDR>") instead.

MovedError is a subclass of ResponseError. The important part here is the error message. When raising MovedError, redis-py removes the MOVED string.

Starting from redis-py 6, the cluster parser exceptions were moved into the base parser, and so it started raising MovedError, without the MOVED string. This was changed in redis/redis-py#3475. You can also see the changelog for 6.0.0b1, which explicitely lists this as a breaking change:

Moved ClusterParser exceptions to BaseParser class (redis/redis-py#3475)

Fix

We keep supporting redis-py <6, but we handle MovedError separately from ResponseError.

[laixintao]

Thanks, this is a nice fix! merged.