Add vector clocks to the structs that are stored in the state store.

[calavera]

Context

This is a precondition to address #1711. Instead of making all the changes at once. I thought it'd be better to introduce vector clocks first, and then start using them as necessary.

What

Implement a simple vector clock using AtomicU64 and add it to the structures that are serialized into the state store.

The clock is not used for anything at the moment, allowing us to introduce CAS semantics gradually over futures changes.

Testing

I'm adding tests for the new builders, and updating existent tests.

Contribution Checklist

• If a Python package was changed, please run make fmt in the package directory.
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