[Feature Request] Use typing.NamedTuple instead of collections.namedtuple for ConsumerRecord

[widow-tamar]

It would be helpful to have type annotations (and possibly default values) for a fundamental datatype of this library.
I'm requesting typing.NamedTuple because it is a first-party alternative that should effectively be a drop-in replacement, and therefore have minimal risk.
I've sketched this out here, with the understanding that this is not a complete or final version of the actual data types.

Per the python docs, typing.NamedTuple supports annotations, default values, and docstrings as of 3.6.1; the repo readme banner indicates 3.8 as the earliest supported version, so I'm assuming this change is safe.

If there's additional work I can do to support this change, please let me know.