feat: add DialContext and EnrollContext for Client

[leslie-fei]

Fixes #541

[leslie-fei]

都改掉提交了

[panjf2000]

startGnetClient 函数现在不需要 ev 了，直接移除掉吧。

还有其他的代码格式化问题也一起解决掉吧，不然 golangci-lint 会报错。

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 79.00%. Comparing base (f6b0d30) to head (fa1e739).
Report is 6 commits behind head on dev.

Files	Patch %	Lines
client_unix.go	83.33%	1 Missing ⚠️
client_windows.go	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #543      +/-   ##
==========================================
- Coverage   79.12%   79.00%   -0.12%     
==========================================
  Files          25       25              
  Lines        2074     2091      +17     
==========================================
+ Hits         1641     1652      +11     
- Misses        299      304       +5     
- Partials      134      135       +1     

Flag	Coverage Δ
unittests	79.00% <86.66%> (-0.12%)	⬇️

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[leslie-fei]

存在的几个data race问题我也修复了下

[panjf2000]

你本地测过了没有？

[leslie-fei]

测过了

[leslie-fei]

改过了, 你看看

[panjf2000]

LGTM
Thanks!