Not Compatible with Domain Reloading turned off

[NickMercer]

Right now, if you turn off Unity's Domain Reloading checkbox, you'll get duplicate listeners on your SignalHub because it's not getting refreshed between play modes.

I made a simple change in my project that fixes this:

First, add a using statement for UnityEditor when you're in the editor:

#if UNITY_EDITOR
using UnityEditor;
#endif

Then, in the static Signals class, replace the hub initialization line with this:

private static SignalHub hub = new SignalHub();

#if UNITY_EDITOR
[InitializeOnEnterPlayMode]
private static void ResetSignalHub()
{
    hub = new SignalHub();
}
#endif

This requires removing the readonly keyword from the static hub, but it's already private in a small static class, so nothing else can get to it and reset it anyway.

This will make sure that the static hub gets re-initialized on play mode enter even if domain reloading is turned off.