refactor io_uring impls

[loongs-zhang]

// Describe your PR here; eg. Fixes #issueNo

Make sure that:

• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed.

[codecov]

Codecov Report

Attention: Patch coverage is 77.61194% with 30 lines in your changes missing coverage. Please review.

Project coverage is 71.06%. Comparing base (5a39680) to head (d4cc0ac).

Files with missing lines	Patch %	Lines
core/src/syscall/unix/mod.rs	73.91%	30 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
+ Coverage   70.67%   71.06%   +0.38%     
==========================================
  Files          69       68       -1     
  Lines        5422     5363      -59     
==========================================
- Hits         3832     3811      -21     
+ Misses       1590     1552      -38     

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