refactor: move routing interfaces into their own files

src/PepperDash.Essentials.Core/Routing/IRmcRouting.cs

@@ -0,0 +1,10 @@
+namespace PepperDash.Essentials.Core.Routing
+{
+    /// <summary>
+    /// Defines a receiver that has internal routing (DM-RMC-4K-Z-SCALER-C)
+    /// </summary>
+    public interface IRmcRouting : IRoutingNumeric
+    {
+        IntFeedback AudioVideoSourceNumericFeedback { get; }
+    }
+}