Tx rollup: update gas model for `Tx_rollup_commitment_repr.Full.compact`

Context

We add a snoop benchmark for Tx_rollup_commitment_repr.Full.compact. We add a logarithmic cost model for this benchmark. The results of running the bench on the reference machine and inferring the parameters of the cost model are attached:

commit-ref.csv

commit-ref.sol

commit-ref-solution.csv

Using this model, we update the earlier conservative upper-bound used in consume_compact_commitment_cost.

Discussion

The cost model inferred from the benches is, in milligas:

cost(compact(messages))  = 811 * |messages|

(where 811 is conservatively rounded up from the inferred 810.46).

The previous, conservative over-approximation was:

cost(add_message(messages, message)) = cost(hashing(32 bytes)) + 2 * |messages| * cost(hashing(64 bytes)) 

In other words, the previous over-approximation would charge ~ 50000 + 100000 * n milligas for each message whereas inferred cost model would charge between 1000n milligas.

Manually testing the MR

Checklist

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