Use items collected from the broadcast receiver for an async function call.
Creates a stream of nonces from verifiers.
This will automatically get the first response from the verifiers.
For each expected sighash, we collect a batch of public nonces from all verifiers. We aggregate and send to the agg_nonce_sender. Then repeat for the next sighash.
Reroutes aggregated nonces to the signature aggregator.
Collects partial signatures from given stream and aggregates them.
Reroutes aggregated signatures to the caller.
Also sends 2 aggregated nonces to the verifiers.