Please address the comments from this code review:

## Overall Comments
- In `TestNonMergeableItemsReplaceOnDuplicate`, both pushed `testItem` instances use `value: 1`, so the assertion that the item is "replaced, not merged" isn’t actually verifiable; consider using different values (e.g., 1 then 2) and asserting that the second value wins to make the behavior observable.
- The `Mergeable[K comparable]` interface doesn’t use its type parameter `K` in the method signature; you could simplify it to `type Mergeable[K comparable] interface{ MergeFrom(old Item[K]) }` → `type Mergeable[K comparable] interface{ MergeFrom(old Item[K]) }` without the type parameter on `Mergeable` itself, or drop the generic on `Mergeable` entirely and just use `MergeFrom(old Item[K])` with the queue’s `K`.
- In tests like `TestMergeablePreservesQueueOrder`, you’re asserting the pulled items with unchecked type assertions (e.g. `first := q.PullBlocking(&stopSignal).(*mergeableItem)`); consider mirroring the safer pattern used elsewhere (`item, ok := ...; require.True(ok)`) to avoid panics and make failures easier to diagnose.

## Individual Comments

### Comment 1
<location path="pkg/dedupingqueue/deduping_queue_test.go" line_range="104-113" />
<code_context>
+	s.Assert().True(merged.flag2, "flag2 should accumulate across three pushes")
+}
+
+func (s *uniQueueSuite) TestNonMergeableItemsReplaceOnDuplicate() {
+	q := NewDedupingQueue[string]()
+	q.Push(&testItem{value: 1})
+	q.Push(&testItem{value: 1})
+
+	s.Assert().Equal(1, q.queue.Len(), "duplicate key should result in one item")
+
+	stopSignal := concurrency.NewSignal()
+	defer stopSignal.Signal()
+	item := q.PullBlocking(&stopSignal)
+	pulled, ok := item.(*testItem)
+	s.Require().True(ok)
+	s.Assert().Equal(1, pulled.value, "non-mergeable item should be replaced, not merged")
+}
+
</code_context>
<issue_to_address>
**issue (testing):** The non-mergeable replacement test does not actually prove replacement vs keeping the existing item

Because both pushed `testItem`s use the same `value`, and `GetDedupeKey` is derived from `value`, this test still passes if the queue keeps the old item instead of replacing it. To verify "replace, not merge" behavior, decouple the dedupe key from the payload (e.g., use a `key int` for `GetDedupeKey` and a separate `value int` that differs between pushes), and then assert that the pulled item has the `value` from the second push. That way the test fails if the queue ever retains the old instance.
</issue_to_address>