SCORU/Node: workers for playing refutation games

Context

Closes #4928 (closed) Closes #4911 (closed)

This MR moves the playing of the refutation game to workers. This is done in two layers:

• Refutation players: worker for handling a refutation game. There will be one of such workers for each refutation that the node has to play.
• Refutation coordinator: a single worker in each node that reacts to L1 heads and manages the refutation players.

Note: the last 3 commits are split for ease of review, but don't build independently. They will be squashed before merging.

Manually testing the MR

CI should be enough