Test: 移除 httpbin 并整理测试

[yanyongyu]

• 使用本地 echo server 代替 httpbin
• 整理或添加了部分测试

[codecov]

Codecov Report

Merging #2110 (36f7e50) into master (7d3c7c4) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2110      +/-   ##
==========================================
+ Coverage   89.56%   89.60%   +0.03%     
==========================================
  Files          46       46              
  Lines        3298     3300       +2     
==========================================
+ Hits         2954     2957       +3     
+ Misses        344      343       -1     

Flag	Coverage Δ
unittests	89.60% <ø> (+0.03%)	⬆️

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see 2 files with indirect coverage changes

[github-actions]

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