NadekoBot.Extensions should now be fully annotated with nullable reference types as well as many classes from NadekoBot.Common

src/NadekoBot/Common/IPlaceholderProvider.cs

@@ -1,6 +1,7 @@
-namespace NadekoBot.Common;
+#nullable disable
+namespace NadekoBot.Common;
 
 public interface IPlaceholderProvider
 {
     public IEnumerable<(string Name, Func<string> Func)> GetPlaceholders();
-}
+}