fix: tighten MCPServer tool result typing #2774

Job	Run time
checks / readme-snippets	14s
checks / pre-commit	49s
checks / test (3.10, lowest-direct, ubuntu-latest)	58s
checks / test (3.11, locked, windows-latest)	1m 32s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 8s
checks / test (3.10, locked, windows-latest)	1m 21s
checks / test (3.11, lowest-direct, windows-latest)	1m 22s
checks / test (3.10, lowest-direct, windows-latest)	1m 31s
checks / test (3.12, lowest-direct, windows-latest)	1m 29s
checks / test (3.10, locked, ubuntu-latest)	59s
checks / test (3.14, lowest-direct, windows-latest)	1m 27s
checks / test (3.12, locked, ubuntu-latest)	1m 1s
checks / test (3.12, locked, windows-latest)	1m 16s
checks / test (3.11, locked, ubuntu-latest)	54s
checks / test (3.13, locked, windows-latest)	1m 19s
checks / test (3.13, lowest-direct, windows-latest)	1m 28s
checks / test (3.14, lowest-direct, ubuntu-latest)	56s
checks / test (3.13, lowest-direct, ubuntu-latest)	55s
checks / test (3.13, locked, ubuntu-latest)	48s
checks / test (3.14, locked, windows-latest)	2m 4s
checks / test (3.14, locked, ubuntu-latest)	1m 58s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 4s
all-green	3s
	26m 36s

Provide feedback