change ModuleVersion to virtual and added a backing field for version

Author: KillStr3aK

managed/CounterStrikeSharp.API/Core/BasePlugin.cs

@@ -40,6 +40,8 @@ public abstract class BasePlugin : IPlugin
     {
         private bool _disposed;
 
+        internal string _version = "<unknown>";
+
         public BasePlugin()
         {
             RegisterListener<Listeners.OnMapEnd>(() =>
@@ -52,7 +54,7 @@ public BasePlugin()
         }
 
         public abstract string ModuleName { get; }
-        public abstract string ModuleVersion { get; }
+        public virtual string ModuleVersion { get => _version; }
 
         public virtual string ModuleAuthor { get; }
 
@@ -650,4 +652,4 @@ protected virtual void Dispose(bool disposing)
             _disposed = true;
         }
     }
-}
+}