Add a pluggable server extension API with MCP Apps #3139

Job	Run time
checks / readme-snippets	14s
checks / docs	40s
checks / pre-commit	50s
checks / test (3.10, locked, windows-latest)	2m 5s
checks / test (3.11, lowest-direct, windows-latest)	1m 35s
checks / test (3.10, lowest-direct, windows-latest)	1m 29s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 18s
checks / test (3.12, locked, windows-latest)	1m 43s
checks / test (3.10, locked, ubuntu-latest)	1m 15s
checks / test (3.12, lowest-direct, windows-latest)	1m 51s
checks / test (3.11, locked, ubuntu-latest)	1m 7s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 8s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.12, locked, ubuntu-latest)	1m 22s
checks / test (3.14, locked, ubuntu-latest)	2m 18s
checks / test (3.13, lowest-direct, windows-latest)	1m 48s
checks / test (3.13, locked, windows-latest)	1m 40s
checks / test (3.11, locked, windows-latest)	1m 19s
checks / test (3.14, lowest-direct, windows-latest)	1m 34s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 29s
checks / test (3.14, locked, windows-latest)	2m 35s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 2s
checks / test (3.13, locked, ubuntu-latest)	1m 5s
all-green	2s
	32m 44s

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