Add ergonomic Client class for testing MCP servers #4097

Job	Run time
checks / pre-commit	36s
checks / readme-snippets	9s
checks / test (3.10, lowest-direct, windows-latest)	2m 12s
checks / test (3.10, lowest-direct, ubuntu-latest)	41s
checks / test (3.10, highest, windows-latest)	2m 11s
checks / test (3.11, highest, ubuntu-latest)	44s
checks / test (3.10, highest, ubuntu-latest)	46s
checks / test (3.12, lowest-direct, ubuntu-latest)	50s
checks / test (3.11, lowest-direct, ubuntu-latest)	44s
checks / test (3.13, highest, ubuntu-latest)	43s
checks / test (3.13, lowest-direct, ubuntu-latest)	44s
checks / test (3.11, highest, windows-latest)	2m 32s
checks / test (3.13, lowest-direct, windows-latest)	2m 44s
checks / test (3.14, highest, windows-latest)	2m 5s
checks / test (3.13, highest, windows-latest)	2m 22s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 9s
checks / test (3.14, highest, ubuntu-latest)	1m 5s
checks / test (3.12, lowest-direct, windows-latest)	3m 18s
checks / test (3.11, lowest-direct, windows-latest)	2m 28s
checks / test (3.12, highest, ubuntu-latest)	53s
checks / test (3.12, highest, windows-latest)	3m 56s
checks / test (3.14, lowest-direct, windows-latest)	2m 19s
	35m 11s

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