Support nested RollbackSynchronizers

[elementbound]

:sparkles: Description

RollbackSynchronizer explores all the children of its configured root, recursively, to look for nodes implementing _rollback_tick. This means that for nested RollbackSynchronizers, multiple synchronizers may end up calling _rollback_tick on the same node.

Use case

Multiple requests were received about having nested RollbackSynchronizers - usually for things that may be implemented with workarounds but can be tedious.

Distribution

netfox core

Notes

• Possible approaches:
  • Add a flag so that RollbackSynchronizer won't look recursively
  • When looking recursively, disregards nodes belonging to a different RollbackSynchronizer
• In theory, nested RollbackSynchronizers are already possible in a way
  • When spawning the nested node at runtime, the parent synchronizer will not gather nodes again
  • This means that the child RBS will have its own set of nodes to manage, distinct from the parent RBS
  • This holds until process_settings() is called for any reason on the root RBS