Gossipsub/score: p3

Context

Implement the p3/p3b scores. N.B.: I used the seen_messages field of the state instead of the message cache. I expect the message cache to be fixed and extended with the first time a message was seen, and the seen_messages field to be removed. Depending on which MR gets merged first I can come back on this particular point/

Solves #5447 (closed)

Manually testing the MR

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