Perform signature collection from counterparties in parallel inside CollectSignaturesFlow.
Note that this does not include any changes to parallel backchain resolution, it involves only the signature collection part.
This change will only be included in ENT. As a result:
The signature of CollectSignaturesFlow needs to remain the same, so that developers can develop against OS and deploy on ENT seamlessly.
Some manual compatibility testing needs to be performed to ensure OS/ENT nodes interoperate successfully, as well as older nodes with newer nodes.
Ideally, if we have managed to build a perf-testing CorDapp that simulates multiple sends/receives, use it to demonstrate the concrete gains from the enhanced flow.