feat(packets): pass nullable to packet serializers

chore: move PacketSerializer types to correct namespace

feat: split packets definitions into separate assembly

Merge pull request #14 from Rutherther/packets-span

Rewrite packets string enumerator to use spans, add Injector for .NET 5+

feat: use ReadOnlySpan for deserialization instead of strings

refactor: split string converters

Merge pull request #16 from Rutherther/packets-list-inline-serializer

Add generation of packet list inline serializer

feat: use StringBuilder Append overloads

Merge pull request #12 from Rutherther/packets

Implement custom packet serializer

feat: add bool type converter