Fix Trap not doing opaque correctly

src/trap.zig

@@ -76,14 +76,14 @@ pub const TrapCode = enum(u8) {
     }
 };
 
-pub const Trap = struct {
+pub const Trap = opaque {
     /// Creates a new trap.
     /// The `Trap` returned is owned by the caller.
-    pub fn init(message: [:0]const u8) Trap {
+    pub fn init(message: [:0]const u8) *Trap {
         return wasmtime_trap_new(message.ptr, message.len + 1);
     }
 
-    pub fn copy(self: *const Trap) Trap {
+    pub fn copy(self: *const Trap) *Trap {
         return wasm_trap_copy(self);
     }