Control Slot in summary cache

### Describe the problem you discovered

Actually if a beacon summary node receive a valid slot, it adds it into the summary cache ets table.
But if a malicious node send multiple times a slot, the beacon summary node will add it again an again in the summary cache leading to a memory overflow and a crash.

### Describe the solution you'd like

To avoid this error, when a beacon summary node receive a slot from a slot node, it can verify in the summary cache if there is already a slot of the same time from the same node. If so the node can aggregate the replication attestations from the new slot into the already existing slot.

No file or test is named. Start by locating the beacon summary node's summary-cache ETS handling and the path that accepts slots; inspect how repeated slots are stored and how replication attestations are represented. Done means repeated slots from the same node and time no longer grow the cache, while their attestations are aggregated.

Written by the indexing model from the issue text.