Proposal: support int8/int16

[felix021]

Due to the limit of dubbo-go-hessian2, int8/int16 in the response can not be decoded.

In this proposal, we would like to make DubboCodec capable of decoding int8/int16, which may need to modify dubbo-go-hessian2

[felix021]

Fixed with:

• https://github.com/apache/dubbo-go-hessian2/pull/366
• https://github.com/kitex-contrib/codec-dubbo/pull/58