It's mostly just needed to interact with FFI and declare some types as Send/Sync. We use it in 3 places: - fixing some FFI on iOS - enabling function-call sy

It's mostly just needed to interact with FFI and declare some types as Send/Sync. We use it in 3 places: - fixing some FFI on iOS - enabling function-call syntax for signals (took this implementation from dtolnay) - implementing Send/Sync for an ID that uses a pointer as a hash (which honestly could be removed in lieu of a usize, now that I'm looking at it)