* interpret legacy and new per-stream format into AirbyteStateMessages
* add ConnectorStateManager stubs for future work
* remove frozen for the time being until we need to hash descriptors
* add validation that AirbyteStateMessage has at least one of stream, global, or data fields
* pr feedback and clean up of the code
* remove changes to airbyte_protocol and perform validation in read_state()
* fix import formatting