Fix potential race conditions in `io_uring` backend.

[ioquatix]

Rework the URing backend to use reference counted waiting nodes, this avoids any potential race condition in CQE processing.

Types of Changes

• Bug fix.

Contribution

• [ ] I added tests for my changes.
• [x] I tested my changes locally.
• [x] I agree to the Developer's Certificate of Origin 1.1.