Store/test: improve liveblocks computation

This MR aims to:

• introduce a liveblock test in the store
• improve the store/test framework to allow crafting real operations
• improve the liveblock computation that could be faulty in edge cases

Manually testing the MR

Green CI.

Run dune exec src/lib_store/unix/test/main.exe -- --title "tezos-store: store (live_blocks)" --verbose with/without the patch to trigger the issue.

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