SCORU: Increase max number of messages per commitment period

Context

Fixes #2373 (closed)

The value is chosen to limit the length of inbox refutation proofs. In the worst case, the length of inbox refutation proofs are logarithmic (in basis 2) in the number of messages in the inboxes during the commitment period.

With the following value, an inbox refutation proof is made of at most 35 hashes, hence a payload bounded by 35 * 48 bytes, which far below than the 32kb limit of a Tezos operation.

Manually testing the MR

CI should stay green.

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