feat: use "in" instead of "ref" in packet serializer

feat: use stackalloc and Span for packet serialization

Merge pull request #47 from Rutherther/feat/pass-nullable

Pass CanBeNull to string serializer and converter

feat(packets): make NullableWrapper a struct for less allocations

feat(packets): pass nullable to packet serializers

Merge pull request #45 from Rutherther/feat/mates

Add support for mates

fix(packets): make nullable wrapper a class

feat(packets): add nullable wrapper to represent a compoud type that may be null as a whole