Stop advertising MCP_* env vars for MCPServer settings; drop pydantic-settings #3646

Job	Run time
checks / readme-snippets	12s
checks / pre-commit	48s
checks / test (3.10, lowest-direct, windows-latest)	1m 57s
checks / test (3.11, lowest-direct, windows-latest)	1m 56s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 20s
checks / test (3.10, locked, ubuntu-latest)	1m 30s
checks / docs	54s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 24s
checks / test (3.11, locked, ubuntu-latest)	1m 19s
checks / test (3.10, locked, windows-latest)	1m 56s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 20s
checks / test (3.14, locked, ubuntu-latest)	1m 26s
checks / test (3.13, lowest-direct, windows-latest)	1m 51s
checks / test (3.12, lowest-direct, windows-latest)	2m 7s
checks / test (3.14, locked, windows-latest)	1m 58s
checks / test (3.14, lowest-direct, windows-latest)	1m 59s
checks / test (3.12, locked, ubuntu-latest)	1m 39s
checks / test (3.13, locked, ubuntu-latest)	1m 21s
checks / test (3.13, locked, windows-latest)	2m 15s
checks / test (3.11, locked, windows-latest)	1m 53s
checks / test (3.12, locked, windows-latest)	1m 51s
all-green	4s
	35m 52s

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