Refactor DnsServer (#2846) #876

Job	Run time
build (macos-latest, host, gcc)	19m 4s
build (macos-latest, esp8266, gcc)	29m 41s
build (macos-latest, rp2040, gcc)	14m 40s
build (ubuntu-latest, esp8266, gcc)	18m 39s
build (ubuntu-latest, host, clang, Host)	24m 49s
build (ubuntu-latest, host, gcc)	22m 6s
build (ubuntu-latest, host, gcc64, Host)	20m 33s
build (ubuntu-latest, rp2040, gcc)	17m 14s
build (windows-latest, esp8266, gcc)	9m 16s
build (windows-latest, host, gcc)	27m 45s
build (windows-latest, rp2040, gcc)	7m 33s
	3h 31m 20s

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