do_after (#1616)

* do_after

Ports (most of) do_after from SS13.
Callers are expected to await the DoAfter task from the DoAfterSystem.
I had a dummy component for in-game testing which I removed for the PR so nothing in game uses do_after at the moment.
Currently only the movement cancellation is predicted client-side.

* Minor do_after doc cleanup

* do_the_shuffle

Fix nullable build errors.

* The last nullable

* Implement NeedHand

Thanks zum.

* nullable dereference

* Adjust the system query

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Shared/GameObjects/ContentNetIDs.cs

@@ -61,6 +61,7 @@
         public const uint THROWN_ITEM = 1054;
         public const uint STRAP = 1055;
         public const uint DISPOSABLE = 1056;
+        public const uint DO_AFTER = 1057;
 
         // Net IDs for integration tests.
         public const uint PREDICTION_TEST = 10001;