Stop advertising MCP_* env vars for MCPServer settings; drop pydantic-settings #3638

Job	Run time
checks / pre-commit	52s
checks / test (3.14, lowest-direct, windows-latest)	2m 1s
checks / test (3.12, lowest-direct, windows-latest)	2m 4s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.13, lowest-direct, windows-latest)	1m 59s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 36s
checks / test (3.10, locked, ubuntu-latest)	1m 29s
checks / test (3.11, lowest-direct, windows-latest)	1m 55s
checks / test (3.10, lowest-direct, windows-latest)	1m 54s
checks / test (3.14, locked, ubuntu-latest)	1m 20s
checks / docs	1m 7s
checks / test (3.13, locked, ubuntu-latest)	1m 19s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 21s
checks / test (3.14, locked, windows-latest)	1m 52s
checks / test (3.13, locked, windows-latest)	2m 1s
checks / test (3.12, locked, windows-latest)	1m 48s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.11, locked, ubuntu-latest)	1m 24s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 25s
checks / test (3.10, locked, windows-latest)	2m 0s
checks / test (3.11, locked, windows-latest)	2m 9s
checks / readme-snippets	12s
checks / test (3.12, locked, ubuntu-latest)	1m 47s
all-green	3s
	36m 23s

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