decode_stack tests: the at-bound union fixture is allowed its large variant

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

packages/cultcache-rs/tests/decode_stack.rs

@@ -273,6 +273,8 @@ struct LargestUnionArm {
     next: Option<Box<LargestUnion>>,
 }
 
+// The fixture is the largest arm the derives accept next to a unit variant, which is the point.
+#[allow(clippy::large_enum_variant)]
 #[derive(Clone, Debug, PartialEq, CultUnion)]
 enum LargestUnion {
     #[cultcache(key = 0)]