Support c-ares, Refactor DNS

[matyhtf]

No description provided.

[codecov]

Codecov Report

Merging #4275 (9651f64) into master (2609899) will increase coverage by 0.10%.
The diff coverage is 79.51%.

@@            Coverage Diff             @@
##           master    #4275      +/-   ##
==========================================
+ Coverage   50.82%   50.92%   +0.10%     
==========================================
  Files          70       70              
  Lines       14183    14222      +39     
==========================================
+ Hits         7208     7243      +35     
- Misses       6975     6979       +4     

Impacted Files	Coverage Δ
src/core/string.cc	78.21% <ø> (ø)
src/core/timer.cc	83.05% <ø> (ø)
src/os/async_thread.cc	67.98% <ø> (-0.88%)	⬇️
src/protocol/websocket.cc	45.45% <ø> (ø)
src/server/base.cc	54.26% <ø> (ø)
src/core/base.cc	73.90% <52.17%> (-1.30%)	⬇️
src/network/dns.cc	87.17% <86.36%> (+0.42%)	⬆️
src/coroutine/system.cc	33.03% <100.00%> (+0.15%)	⬆️
src/server/port.cc	50.27% <0.00%> (+0.27%)	⬆️
... and 3 more

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