Motivation:

`RedisCommandExecutor` was a complex and "wordy" name that was not 100% clear as to how it relates to other types.

`RedisConnection` also has not had a strong use case shown for it to exists as a separate protocol - using up a great name for the "out of the box" implementation.

Result:

`RedisClient` instead of `RedisCommandExecutor` is more clear as to what it is, in Redis terminology, a communication client.

`RedisConnection` as a concrete class provides an identifiable basic block for making connections to Redis.

`RedisConnection` also saw some fixes to `close()` while having some names and comment blocks tweaked for updated naming.