dispatch: Fix intermittent TestMuxPublish issue (#1412)

* Dispatch: Assertify TestMuxPublish

* Dispatch: Fix errDispatcherJobsAtLimit test fails

This test would fail intermittently when the jobs queue drained quickly
enough.
This sets the overload ceiling based on the default settings, and seems
a safe way of ensuring we get an error every time.

It adds a done channel guard around the goro test because otherwise
we'll get a panic occassionally when the goro outlives TestMaxPublish

* Dispatch: Add test for Publish receiving data

* Dispatch: Publish to all subscribers

dispatch/dispatch.go

@@ -180,11 +180,9 @@ func (d *Dispatcher) relayer() {
 				continue
 			}
 			for i := range pipes {
-				select {
-				case pipes[i] <- j.Data:
-				default:
-					// no receiver; don't wait. This limits complexity.
-				}
+				go func(p chan any) {
+					p <- j.Data
+				}(pipes[i])
 			}
 			d.rMtx.RUnlock()
 		case <-d.shutdown: