SCORU/Node: use blocks cache

Use a LRU cache for the Layer 1 blocks.

The cache is used by the rollup node itself and also its injector (see MR !5250 (merged)).

Incidentally fixes #3139 (closed).

This is a prerequisite for:

• !5681 (merged)
• !5690 (merged)
• !5250 (merged)

Manually testing the MR

There should be no observable changes in:

dune exec tezt/tests/main.exe -- -f sc_rollup.ml

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Provide automatic testing (see the testing guide).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR