feat(volo-http): add CommonStats and ServerStats struct to record lifecycle timings

[Joshuahoky]

Motivation

Volo-http currently lacks visibility into key HTTP lifecycle timings, such as:

• Time to read request headers and body
• Time spent handling the request
• Time to write the response body

Solution

Added ServerStats in volo-http/src/context/server.rs to store timestamps for:

• request header read start/finish
• request body read start/finish
• handler execution start/finish
• response body write start/finish

Also instrumented the request handling flow to populate the ServerHandleStart / Finish fields of ServerStats

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.85%. Comparing base (c971091) to head (7ca20c8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #649      +/-   ##
==========================================
+ Coverage   44.84%   44.85%   +0.01%     
==========================================
  Files         162      162              
  Lines       20078    20081       +3     
==========================================
+ Hits         9003     9007       +4     
+ Misses      11075    11074       -1     

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[shenyj3]

这里应该不是 handle start，更像是 recv end，http request 已经收完了。

service.inner.call() 只是会走到 service 里，但是不代表已经开始进入业务逻辑了，中间还有 middleware、route、param extract 等。

真正的 handler start 要到 volo-http/src/server/handler.rs#L77 这里了。

[shenyj3]

同上，这里是 send start 而不是 handle finish。