feat(core): split raw client and managed client as well as packet handlers

Resolves #65

feat(tests): add tests structure

feat!(core): make some classes internal

Merge pull request #12 from Rutherther/packets

Implement custom packet serializer

chore: remove NosCore dependency

chore: fix line endings

Merge branch 'in-packet-serialize' into 'main'

Serialize IN packet

See merge request Rutherther/nos-smooth!3

tests: add tests for in packet serializer