SCORU: Require conflicting commitments hashes to start game

Context

Since get_conflict_point is not gas friendly, we stop using it in the protocol when we start a game. This computation must be done off-chain.

Related to #4372 (closed). This MR partially fixes the issue of gas-unfriendly linear traversals.

TODO:

• add tests (negative & storage)
• rebase + backport

Manually testing the MR

CI

owner: @sribaroud

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
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• Provide automatic testing (see the testing guide).
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