scheduler: spawn_monitor / spawn_monitor_with — monitor registered on the child's slot before publish, so the Down always carries the real reason (spawn-then-monitor could race to NoProc); tests; channel test uses it

src/lib.rs

@@ -89,9 +89,9 @@ pub use runtime::{init, Config, Runtime, RuntimeHandle};
 pub use scheduler::{
     block_on_io, cancel_timer, request_shutdown, request_stop, run, self_pid, send_after,
     send_after_named, send_after_named_wall, send_after_wall, sleep, sleep_wall, spawn, spawn_addr,
-    spawn_addr_with, spawn_under, spawn_under_with, spawn_with, try_spawn, try_spawn_under_with,
-    wait_readable, wait_readable_timeout, wait_writable, wait_writable_timeout, yield_now, FdArm,
-    JoinError, JoinHandle, SpawnError, SpawnOpts,
+    spawn_addr_with, spawn_monitor, spawn_monitor_with, spawn_under, spawn_under_with, spawn_with,
+    try_spawn, try_spawn_under_with, wait_readable, wait_readable_timeout, wait_writable,
+    wait_writable_timeout, yield_now, FdArm, JoinError, JoinHandle, SpawnError, SpawnOpts,
 };
 pub use supervisor::{ChildSpec, OneForOne, Restart, Shutdown, Signal, Strategy};
 pub use timer::TimerId;