refactor: rename packages and files in dagger-common serde

[Meghajit]

Dagger will soon have a new data source for Parquet files. For deserialization of records, it will continue to use dagger-common module and the handler classes within.

Currently, the package names have keywords like proto and protohandler which are kind of misleading as the same handler classes will have methods to do parsing for both Protobuf objects as well as SimpleGroup objects.

Hence, there is a need to refactor some of these package names and classes inside the dagger-common module to better reflect its responsibility.

This issue is meant to do that. No functional change is required. This will only be a refactor.