Add ergonomic Client class for testing MCP servers #4111

Job	Run time
checks / pre-commit	34s
checks / readme-snippets	11s
checks / test (3.12, lowest-direct, ubuntu-latest)	52s
checks / test (3.11, locked, ubuntu-latest)	43s
checks / test (3.12, locked, ubuntu-latest)	54s
checks / test (3.10, lowest-direct, windows-latest)	2m 22s
checks / test (3.10, lowest-direct, ubuntu-latest)	48s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.12, lowest-direct, windows-latest)	3m 27s
checks / test (3.10, locked, ubuntu-latest)	48s
checks / test (3.10, locked, windows-latest)	2m 21s
checks / test (3.11, locked, windows-latest)	2m 47s
checks / test (3.12, locked, windows-latest)	3m 25s
checks / test (3.13, lowest-direct, ubuntu-latest)	42s
checks / test (3.11, lowest-direct, windows-latest)	2m 32s
checks / test (3.14, locked, ubuntu-latest)	2m 15s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.13, locked, ubuntu-latest)	43s
checks / test (3.14, lowest-direct, windows-latest)	2m 20s
checks / test (3.13, locked, windows-latest)	2m 55s
checks / test (3.13, lowest-direct, windows-latest)	2m 24s
checks / test (3.14, locked, windows-latest)	3m 8s
	38m 11s

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