perf(storage): gRPC zerocopy codec (#10888)

* perf(storage): gRPC zerocopy codec

Replace the current custom codec for ReadObjectResponse with a
CodecV2 that can handle data split across multiple buffers.

Unit tests pass but need to finish up some stuff to get the
end-to-end working.

* add test with buffer splits

* wire up end-to-end

* remove extra lines

* improve tests, fix bugs

* fix Read issues

* fix ref issue

* fix unmarshalling for later messages

* checkout mod and sum from main

* fix typo, vet

* avoid embedding interface

* change databufs to value

* fix remaining code review comments

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Co-authored-by: Frank Natividad <[email protected]>