Add timeout for http request roundtripper

[xiaokangwang]

This merge request add timeout for http round tripper to avoid attack with slow request. Beaware in typical usage, the requests are already authenticated before it reachs V2Ray.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 35.60%. Comparing base (346ca66) to head (603c0ee).

Files	Patch %	Lines
...ort/internet/request/roundtripper/httprt/httprt.go	0.00%	7 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2996      +/-   ##
==========================================
+ Coverage   35.59%   35.60%   +0.01%     
==========================================
  Files         729      729              
  Lines       41613    41619       +6     
==========================================
+ Hits        14812    14820       +8     
- Misses      25167    25169       +2     
+ Partials     1634     1630       -4     

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