Add private protected ctors to McpClient and McpServer to prevent external derivation #2238

Job	Run time
build (ubuntu-latest, Release)	6m 45s
build (ubuntu-latest, Debug)	7m 4s
build (macos-latest, Debug)	6m 11s
build (macos-latest, Release)	4m 33s
build (windows-latest, Debug)	11m 32s
build (windows-latest, Release)	10m 41s
publish-coverage / publish-coverage	1m 1s
	47m 47s

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