Restructured the project structure back to the way it was, there's no reasonable way to split the modules

src/NadekoBot/_common/_Extensions/BotCredentialsExtensions.cs

@@ -0,0 +1,10 @@
+namespace NadekoBot.Extensions;
+
+public static class BotCredentialsExtensions
+{
+    public static bool IsOwner(this IBotCredentials creds, IUser user)
+        => creds.IsOwner(user.Id);
+    
+    public static bool IsOwner(this IBotCredentials creds, ulong userId)
+        => creds.OwnerIds.Contains(userId);
+}