feat: implements text/event-stream(SSE) MIME parser

[jizhuozhi]

Ⅰ. Describe what this PR did

Implements an EventStream for common SSE(text/event-stream) parsing.

And add sse-timing plugin for tracing timestamp that each event received in higress as an example. As an alternative implementation of the server-timing protocol (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server-Timing). It's useful to profile AI backend latency which uses event-stream MIME type.

Ⅱ. Does this pull request fix one issue?

None

Ⅲ. Why don't you add test cases (unit test/integration test)?

As an example, there is no need to integration test, but has an unit test in event_stream.rs

Ⅳ. Describe how to verify it

There is a docker-compose.yml in plugin directory, with a go server backend which provides sse response, up it and then just use broswer to open http://localhost:10000, you could see events in dev-tools.

Ⅴ. Special notes for reviews

[jizhuozhi]

An alternative PR of #1361, but not as a publish plugin

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.62%. Comparing base (ef31e09) to head (72c9fa9).
Report is 164 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1416      +/-   ##
==========================================
+ Coverage   35.91%   43.62%   +7.71%     
==========================================
  Files          69       76       +7     
  Lines       11576    12320     +744     
==========================================
+ Hits         4157     5375    +1218     
+ Misses       7104     6613     -491     
- Partials      315      332      +17     

see 69 files with indirect coverage changes

[johnlanni]

cc @007gzs

[jizhuozhi]

@johnlanni @007gzs PTAL

[007gzs]

使用的变量建议去掉开头下划线，找了下clippy 好像还没支持 rust-lang/rust-clippy#4239

[007gzs]

LGTM