chore: use errors.Is and errors.Join for customized errors

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.34%. Comparing base (29dca4f) to head (0ad8b95). Report is 2 commits behind head on dev.

Files with missing lines	Patch %	Lines
engine_unix.go	66.66%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #640 +/- ## ======================================= Coverage 80.34% 80.34% ======================================= Files 21 21 Lines 2096 2096 ======================================= Hits 1684 1684 Misses 285 285 Partials 127 127 ``` | [Flag](https://app.codecov.io/gh/panjf2000/gnet/pull/640/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andy+Pan) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/panjf2000/gnet/pull/640/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andy+Pan) | `80.34% <80.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andy+Pan#carryforward-flags-in-the-pull-request-comment) to find out more.

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