Consider simplifying the aggregation logic

[iansuvak]

Context and scope
Current POC implementation of the signature aggregation was based on the existing logic in the relayer. We should consider simplifying and/or improving the logic while working through the other MVP issues. Particularly #382 as it will be modifying the code flow.

• look at simplifying the logic in relayer/network_utils.go based on feedback in Move relayer to subfolder #411

Discussion and alternatives
Another existing implementation of the signature aggregation functionality that we can reference is in the subnet-evm repo.

Consider immediately unmarshalling signatures when received instead of in aggregateSignatures
Open questions