DNS: Use cache for NXDOMAIN (rcode 3 error)

[patterniha]

First, I have to thank @Fangliding for his guidance on #4558 (comment).

I mistakenly think that the problem is related to log, but in fact log is just log and has nothing to do with performance.

in #3784 @Fangliding change the original code err != errRecordNotFound to err == nil || err == dns_feature.ErrEmptyResponse To be more accurate.

but in android some apps send thousands of requests in a matter of seconds, that return NXDOMAIN.

This causes performance to drop drastically, and many people have complained about this.

So I also added NXDOMAIN to the modes that should use cache.

[xqzr]

相关链接：
https://t.me/projectXray/4241610
https://t.me/projectXray/4241636

[Meo597]

家用路由器上的dnsmasq不会面临此问题，因为它的upstream就是tcp udp

鉴于xray特有场景，应像isp的递归dns一样，防御nxdomain flood

针对nxdomain应不遵守rfc，强制缓存10或者60秒

过大的值会导致网站管理员遇到困扰不得不重启xray

[RPRX]

话说我之前改 DNS 时也注意到了，ray 每多支持一种 DNS 查询方式就是 copy 整份代码，这挺劣质的，有空把它们改为复用吗？

[Meo597]

话说我之前改 DNS 时也注意到了，ray 每多支持一种 DNS 查询方式就是 copy 整份代码，这挺劣质的，有空把它们改为复用吗？

#5248