async queue:add api about length

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 76.17%. Comparing base (4b0532f) to head (64fe2e1).

Files	Patch %	Lines
src/utils/async_queue.c	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2080 +/- ## ========================================== - Coverage 76.22% 76.17% -0.06% ========================================== Files 104 104 Lines 18447 18454 +7 ========================================== - Hits 14061 14057 -4 - Misses 4386 4397 +11 ```

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