[Chronik] Refactor serialization, add db_serialize and db_deserialize.

Summary:
We will use de-/serialization a lot, so having a module with nice error handling is very helpful.

The db_ prefix indicates that this serialization is only meant for data going in and out of the database.

This also makes it much simpler to move to another serialization format if ever needed.

Test Plan: ninja check-crates

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11798