Proto: mempool check for consensus vote's minimal slots

What

Under aggregate_attestation feature flag, the mempool is computing each delegate minimal slots when flushing and use this pre-computed data structure to refuse consensus operations with non-minimal slots.

Note that computing minimal slots for all 3 allowed levels takes around 15ms on my laptop (m3 macbook).

Why

It is necessary to prevent a malicious peer to flood the network with consensus operations with non-minimal slots. The previous solution to prevent this behaviour was to slash delegates sending consensus operations with non-minimal slots. Since we are removing slots from the signed payload for consensus operations signed by BLS keys, we cannot rely on this solution anymore.

This requirement is temporary and won't be necessary once "all baker attest all block" is activated.

Closes #7652 (closed)

How

Manually testing the MR

Checklist

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