Use forkInstance + Fiber.interrupt (which awaits) instead of
runCallbackInstance + interruptUnsafe (fire-and-forget) for
subscribeAll. This ensures the fiber completes before layer
invalidation, allowing the RcMap refCount to drop to 0.
subscribeAll now delivers InstanceDisposed as the last callback
message via Effect.ensuring when the fiber is interrupted during
disposal, but not on manual unsubscribe.
Add priority support to registerDisposer so Bus can interrupt
subscription fibers (priority -1) before layer invalidation
(priority 0).
Add forkInstance helper to effect/runtime that returns a Fiber
instead of an interrupt function.
0c2b5b2c39