Proto,tx_rollup,node: A first node that track head and stores inboxes

Context

This MR introduces a Node that maintains a (persisted) state for messages, inboxes and the tracked tezos head. The storage of inboxes (and messages) works by reacting to block streams and capturing operations related to the batch's submission.

I have taken the liberty of appointing reviewers but feel free to add or withdraw if you feel your review is not relevant (or you don't have time).

Manually testing the MR

dune exec tezt/tests/main.exe -- --file tx_rollup.ml --verbose

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