[songgaoye]

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

MPSCQueue<T>::Enqueue(const T&) and MPSCQueue<T>::Enqueue(T&&) duplicate
the node allocation and enqueue logic. The only behavioral difference is
whether the task value is copied or moved.

What is changed and the side effects?

Changed:

• Extract the shared enqueue logic into a private forwarding helper.
• Preserve copy semantics for lvalue inputs and move semantics for rvalue
  inputs.

Side effects:

• No intended behavioral change.

• Performance effects:

  No expected performance impact. Node allocation and queue operations are
  unchanged.

• Breaking backward compatibility:

  No API or ABI changes.

---

Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

🟢 Approval recommended

The focused refactor preserves value categories, allocation, and synchronization, with no unresolved findings.

No open issues 🎉

What changed in this PR

Consolidates the duplicated MPSCQueue enqueue paths into a private forwarding helper without changing the public API or queue behavior.

Changes:

• Shares node allocation, initialization, and enqueue logic between both overloads.
• Preserves copy semantics for lvalues and move semantics for rvalues.

File	Description
src/​butil/​containers/​mpsc_queue.h	Adds EnqueueInternal and delegates both enqueue overloads to it.

_{Review effort: Balanced}