Validation of a large volume of incoming ATXs within a limited timeframe

[mathcrypto]

Issue description:

The reason why we need to validate a large volume of ATXs in a limited time frame is because we have lots of more nodes joining the network(scaling issue). And one of these issues is that we have a parameter that we want to have the committee size on average 50 members per layer. Every node gets at least one vote. So there will be more than 50 per layer.

Proposed Solutions:

1. Naive ATX combining method: this method combines multiple post-proofs into a single ATX, so instead of collecting ATXs from every individual node, you just collect their post-proofs and you put them in a single list.
   Even the ATX combining method reduces it temporarily, if the network keeps growing and we see actually more nodes that are operated by different people, we run into the same problem again, because you will not randomly combine someone’s identity with somebody else.

2. Increase number of proposals per committee: This method however increases the latency.

3. Increase epoch length:

See ATX incentivization#297