feat: support getChild method

[czy88840616]

• 1、优化格式化时间函数，增了 benchmark
• 2、增加了 getChild 方法，可以通过这个方法获取到一个新的 logger 实例，child logger 复用所有的 parent logger 的 transports，可以通过参数增加一些额外的 meta 属性，便于在 format 中做自定义展示。

[codecov-commenter]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (eba2e0c) 70.57% compared to head (a9384ab) 70.44%.

Files	Patch %	Lines
src/logger.ts	47.36%	10 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #114 +/- ## ========================================== - Coverage 70.57% 70.44% -0.13% ========================================== Files 11 11 Lines 1244 1269 +25 Branches 384 385 +1 ========================================== + Hits 878 894 +16 - Misses 335 344 +9 Partials 31 31 ```

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