feat: stringify buffers 🧵

previously Buffers are stringified as objects - eg:

> JSONSerializer({ word: Buffer.from('example') })
{"word":{"type":"Buffer","data":[101,120,97,109,112,108,101]}}

this proposal updates the default JSON Serializer to stringify buffers - eg:

> JSONSerializer({ word: Buffer.from('example') })
{"word":"example"}