SCORU/Node: use local information to compute reorganizations

Context

Fixes #4903 (closed).

Use information stored locally by the rollup node about the old chain to compute reorganizations. This prevents the rollup node from stopping even if some blocks become unavailable on the Layer 1 Tezos node.

Manually testing the MR

dune exec tezt/tests/main.exe -- -f sc_rollup.ml  -t 'Alpha: arith - rollup node - correct handling of commitments (handles_chain_reorgs_missing_blocks)'