Add protocols for entries?

Make each type of entry class implements a group of protocols, then even an entry is initialized from a class different from any entryClass in Charts library is still useable

Review the entry classes and the code paths that require a type listed in the Charts library's entryClass set. Determine the shared protocols needed for each entry type and how custom entry classes are currently rejected or accepted. Done means entries initialized from classes outside the built-in set remain usable without breaking existing entry behavior.

Written by the indexing model from the issue text.