Create a new NetplaySession each time we try to join a netplay game. Hold onto it in NetplayManager so its available to the different activities that need to access it. Close the session when backing out of the netplay UI. Some guardrails in case things go out of sync: creating a session closes the old one if it is still around for some reason, finalizer in NetplaySession to release native resources if not closed explicitly for some reason. Profiling done to ensure all kotlin and native objects are successfully cleared / garbage collected.
