Convert coordinator/substrate/db to use create_db macro

[davidjohnbell]

Description

This is a continuation of pr #408. SubstrateDb was split into BlockDb, EventDb, SessionDb, and BatchDb, some helper methods to convert to/from the expected type were removed as they're covered by the macro.

Considerations

• Helper function handled was renamed to is_unhandled. Calling code was largely in the form if !SubstrateDb::handled(...) { ... }, removing the negation and changing the name helps align the code with the intent.
• handle_event could be refactored into a simple set method, I noticed that the calling code often performs the necessary checks however I didn't feel comfortable making this change due to some async statements that could break the previous assertions.

[davidjohnbell]

I'm resolving the merge conflicts 😓. For some reason git assured me I was up to date on my branch...

[davidjohnbell]

closing in favor of pr #436