Rollup node: fix outbox registration in case of reorg

What

Fixes #7730 (closed)

This MR adds a test for and fixes an issue where outbox messages can disappear in case of a reorg, if they are overwritten by messages of a reorged block.

How

We just overwrite the outbox messages with the correct ones for block of a reorg even if we have already handled them.

Manually testing the MR

dune exec tezt/tests/main.exe -- --file sc_rollup.ml outbox reorg