wiggle: convenient syntax for marking all funcs async

crates/wiggle/tests/atoms_async.rs

@@ -7,9 +7,7 @@ use wiggle_test::{impl_errno, HostMemory, MemArea, WasiCtx};
 
 wiggle::from_witx!({
     witx: ["$CARGO_MANIFEST_DIR/tests/atoms.witx"],
-    async: {
-        atoms::{int_float_args, double_int_return_float}
-    }
+    async: *,
 });
 
 impl_errno!(types::Errno);