Support Redis-rb v5

[hieuk09]

This is an attempt to fix #281. This PR was also tested using the test suite of our service.

There are a few decisions I made regarding this PR, please let me know if it's not appropriate:

1. Error from Redis now contains the redis connection URL

• To fix this, I created MockRedis::Error module which decorate Redis::CommandError and related errors with the connection URL
• I replace most of the Redis::CommandError with the new module wrapper

2. Some methods now return integer as output instead of boolean and exists_returns_integer is removed

• I replace the output as is

3. Interfaces of most data structures (Hash, Set, ...) now validate type to be 4 main primitive types

• assert_type is added to validate the arguments. Currently it doesn't look very clean, so any improvements would be great.

4. sadd, srem now support multiple arguments
5. Transaction: multi now needs to call with a block and discard/exec cannot be called outside that block anymore

• I tried to refactor the logic to make the tests pass, but I'm not entirely confident that it works correctly

[hieuk09]

These changes mimic how redis-rb handles the number conversion

[hieuk09]

This change is tested only with MockRedis and not with the multiplexer.

[hieuk09]

I can't access connection URL inside Stream object so I need to rescue the error & wrap it here

[sds]

Phenomenal effort—thank you.

If after release bugs are found related to this change, I will redirect any issues opened to you for the time being (unless trivial to address myself). Thanks again.