Restructure `IMcpEndpoint`, `IMcpClient`, and `IMcpServer` #703

Job	Run time
build (ubuntu-latest, Debug)	3m 59s
build (macos-latest, Release)	3m 27s
build (macos-latest, Debug)	2m 53s
build (ubuntu-latest, Release)	3m 19s
build (windows-latest, Release)	8m 4s
build (windows-latest, Debug)	9m 38s
publish-coverage / publish-coverage	42s
	32m 2s

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