[3.0] 重构 RequestContext

[Yurunsoft]

• 把 flag 改名为 id
• 引入新的上下文对象类 ContextData，并支持所有环境下的 defer()
• Swoole 环境下的上下文，不直接使用 Swoole 上下文，也是使用 ContextData
• 计划废弃 IMI.REQUEST_CONTENT.DESTROY 事件，可以用 defer() 代替。将在连接中心代替旧版连接池后正式废弃！

[codecov]

Codecov Report

Attention: 26 lines in your changes are missing coverage. Please review.

Comparison is base (3043be4) 66.62% compared to head (0fb558b) 66.71%.

Files	Patch %	Lines
...nts/swoole/src/Context/CoroutineContextManager.php	67.92%	17 Missing ⚠️
src/Core/Context/DefaultContextManager.php	70.00%	6 Missing ⚠️
src/RequestContext.php	81.25%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.0     #654      +/-   ##
============================================
+ Coverage     66.62%   66.71%   +0.09%     
- Complexity    10769    10777       +8     
============================================
  Files           870      871       +1     
  Lines         29222    29244      +22     
============================================
+ Hits          19469    19511      +42     
+ Misses         9753     9733      -20     

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