Avoid buffer copies in RedisStateMachine

[jeffreye]

Feature Request

Is your feature request related to a problem? Please describe

This will be a performance improvement for all operations

Describe the solution you'd like

Less buffer, less copy. We can reuse the same buffer from Netty by slicing buffer.

Describe alternatives you've considered

NA

Teachability, Documentation, Adoption, Migration Strategy

If you can, explain how users will be able to use this and possibly write out a version the docs.
Maybe a screenshot or design?

[mp911de]

Looking at the approach, it isn't exactly zero-copy, it's less copy as UnpooledDirectByteBuf holds a buffer and a tmpNioBuf. In any case, it's an improvement.