feat: expose iouring register buffers interface

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (79b260b) 78.59% compared to head (b7bc03f) 78.97%.

Files	Patch %	Lines
util/fibers/uring_proactor.cc	0.00%	4 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #204 +/- ## ========================================== + Coverage 78.59% 78.97% +0.38% ========================================== Files 100 100 Lines 7574 7521 -53 ========================================== - Hits 5953 5940 -13 + Misses 1621 1581 -40 ```

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