Proto/test: unflakes the inactivity

What

In the protocol tests, the scenario_bake helpers did not account for attestation in measuring delegates activity. This led to flaky test for the autostaking, as baker having attested but not baked where deemed inactive in the model and not in the protocol. Thus the model unstaked the funds while the protocol didn't.

Why

Although a pinch of flakiness can make the salt of life, it was decided it's not welcome in the CI. Let's melt the flakes.

How

keeping track of attesters and update their activity cycle.

Manually testing the MR

dune exec src/proto_alpha/lib_protocol/test/integration/main.exe -- --file src/proto_alpha/lib_protocol/test/integration/test_scenario_autostaking.ml --title 'Alpha: Test auto-staking with overdelegation' --loop used to fail rapidely on master.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR