Remove redundant MinGW `inet_ntop` and `inet_pton`, fix `INVALID_SOCKET` tautology #83

Job	Run time
Build & test (ubuntu-latest, release)	25s
Build & test (ubuntu-latest, debug)	22s
Build & test (windows-latest, release)	1m 16s
Build & test (windows-latest, debug)	1m 15s
Build & test (macos-latest, release)	28s
Build & test (macos-latest, debug)	16s
	4m 2s

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