Use `ByteBuffer` for `RESPValue` data storage
From the proposal discussion thread: https://forums.swift.org/t/discussion-nioredis-nio-based-redis-driver/22455/11
Change
public enum RESPValue {
case .simpleString(String)
case .bulkString([UInt8])
}
to
public enum RESPValue {
case .simpleString(ByteBuffer)
case .bulkString(ByteBuffer?)
}```