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

Merge pull request #12 from Rutherther/packets

Implement custom packet serializer

feat: add support for optional parameters

fix: set enumerator level ReachedEnd to null if not known

feat: do not remove prepared level on pop level

feat: add base packet types converting