- allow the creation of arbitrary Lamport clocks, freeing the way to new entities and removing Bug specific (upper layer) code.
- generalize the memory-only and persisted Lamport clocks behind a common interface
- rework the tests to provide reusable testing code for a Repo, a Clock, a Config, opening a path to add a new Repo implementation more easily
- test previously untested components with those new tests
Note: one problem found during this endeavor is that `identity.Version` also need to store one time + Lamport time for each other Entity (Bug, config, PR ...). This could possibly done without breaking change but it would be much easier to wait for https://github.com/MichaelMure/git-bug-migration to happen.
