优化 ArrayUtil::isAssoc

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (dd9c50a) 63.03% compared to head (0aeddab) 66.58%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 3.0 #645 +/- ## ============================================ + Coverage 63.03% 66.58% +3.54% Complexity 10737 10737 ============================================ Files 867 867 Lines 29146 29151 +5 ============================================ + Hits 18373 19409 +1036 + Misses 10773 9742 -1031 ``` | [Files](https://app.codecov.io/gh/imiphp/imi/pull/645?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=imiphp) | Coverage Δ | | |---|---|---| | [src/Util/ArrayUtil.php](https://app.codecov.io/gh/imiphp/imi/pull/645?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=imiphp#diff-c3JjL1V0aWwvQXJyYXlVdGlsLnBocA==) | `100.00% <100.00%> (ø)` | | ... and [74 files with indirect coverage changes](https://app.codecov.io/gh/imiphp/imi/pull/645/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=imiphp)

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