Object.Equals(object) overrides should not throw

Especially not if you pass null.  null is simply not equal to this, that's all.  The post condition is satisfiable; you can return false.

src/BizHawk.Common/Bit.cs

@@ -83,7 +83,7 @@ namespace BizHawk.Common
 
 		public override bool Equals(object? obj)
 		{
-			return this == (Bit) (obj ?? throw new NullReferenceException()); // this is probably wrong
+			return obj is Bit b && this == b;
 		}
 	}
-}
+}