refactor: proxy validator

[1zun4]

To improve accuracy when checking proxy health, we now query a Minecraft server instead. This ensures that the proxy supports Minecraft communication. There are many providers and proxies that only support HTTP/HTTPS communication, so this is the best way to check. This also has the side effect of giving us accurate ping information, which may be useful to implement in the GUI in the future.

Logging:

(LiquidBounce) Request ping server via proxy... [smart.eu-fra.liquidproxy.net:1080]
(LiquidBounce) Resolved ping server [ping.liquidproxy.net]: ping.liquidproxy.net/178.63.18.138:25565
(LiquidBounce) Sent query request via proxy [smart.eu-fra.liquidproxy.net:1080]
(LiquidBounce) Proxy Metadata [smart.eu-fra.liquidproxy.net:1080]: 45.88.109.232
(LiquidBounce) Proxy Ping [smart.eu-fra.liquidproxy.net:1080]: 16 ms
(LiquidBounce) Proxy Info [smart.eu-fra.liquidproxy.net:1080]: 45.88.109.232 [DE, AS44486 Oliver Horscht is trading as "SYNLINQ"]
(LiquidBounce) Checked proxy [smart.eu-fra.liquidproxy.net:1080]
(LiquidBounce) Successfully saved config 'proxy'.