[FEATURE REQUEST] No nice way to set priority on !Send tasks

[awused]

Right now there is no safe binding exposed to set the priority on !Send callbacks except spawning a !Send channel which is awkward - it took me a bit of digging to even realize that was an option. idle_add_local and timeout_add_local don't expose a priority parameter, idle_source_new, timeout_source_new, do take priorities but they require Send since Source is Send.

[sdroege]

Do you want to provide a PR for this? You'd use a ThreadGuard here for the implementation so that it simply panics at runtime if it happens to be sent to another thread.

[awused]

I might but probably not any time soon, I was able to temporarily work around this by raising the priority of other things, but it's left me with less room to maneuver. If you have a good idea of how you would want it implemented that would probably be a lot faster.