SCORU/Node: allow to run rollup nodes concurrently for different protocols

Context

This MR makes the rollup node only monitor blocks of its own protocol and wait to see one before acquiring the lock (and stops on protocol upgrade). This effectively allows for multiple rollup nodes to be started concurrently, taking over when one stops.

Note: This mechanism does not allow to catch up on a protocol migration that a rollup node missed. It will be deprecated once the protocol agnostic node is ready which handles dispatching more gracefully.

This MR also fixes the migration test that was problematic for !8846 (closed).

Manually testing the MR

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