Improve RequestInfo and ResponseInfo types

[aoberoi]

currently, these types are used in many different contexts and the differences are mostly based on unstated convention.

sometimes it would be more useful to have string bodies than buffers

sometimes the properties that are undefined should be defined, and the rest of the time its a pain to explicitly set them to undefined

sometimes another data type houses the information needed like the timestamps

it would be useful to design a hierarchy of types where the relationships are well structured and defined. perhaps different types used in matching versus actual versus proxy recorded.

[aoberoi]

some hints for this added in #47