Convert Reactor.Shared to a source-only nuget package

Reactor.Networking.Shared/ReactorProtocolVersion.cs

@@ -0,0 +1,22 @@
+namespace Reactor.Networking;
+
+/// <summary>
+///     Version of the Reactor.Networking protocol format.
+/// </summary>
+public enum ReactorProtocolVersion : byte
+{
+    /// <summary>
+    ///     First public Reactor Protocol version.
+    /// </summary>
+    V2 = 1,
+
+    /// <summary>
+    ///     Version introducing vanilla server support, syncer concept and registries.
+    /// </summary>
+    V3 = 2,
+
+    /// <summary>
+    ///     Latest version.
+    /// </summary>
+    Latest = V3,
+}