Handle should be an enum or packed struct

[pfgithub]

That way it will support ==. enum is preferred because then == .nil will work. packed struct is a one line and probably nonbreaking change.

eg:

-   return extern struct {
+   return enum (Id) {
...
-       id: Id = 0,
-       pub const nil = Self{ .id = 0 };
+       nil = 0,
+       _,
+       pub fn id(self: Self) Id {
+           return @intFromEnum(self);
+       }

And then you can do:

if (some_handle == .nil) ...
if (handle_a == handle_b) ...