Gracefully terminate active sessions during StreamableHTTP shutdown #1377

Job	Run time
checks / pre-commit	32s
checks / readme-snippets	17s
checks / test (3.10, locked, ubuntu-latest)	47s
checks / test (3.11, lowest-direct, windows-latest)	3m 1s
checks / test (3.10, lowest-direct, ubuntu-latest)	50s
checks / test (3.10, lowest-direct, windows-latest)	2m 54s
checks / test (3.11, lowest-direct, ubuntu-latest)	50s
checks / test (3.13, lowest-direct, windows-latest)	2m 49s
checks / test (3.11, locked, windows-latest)	2m 29s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.13, locked, windows-latest)	2m 35s
checks / test (3.13, locked, ubuntu-latest)	42s
checks / test (3.10, locked, windows-latest)	2m 38s
checks / test (3.12, locked, windows-latest)	3m 30s
checks / test (3.12, lowest-direct, ubuntu-latest)	55s
checks / test (3.12, locked, ubuntu-latest)	51s
checks / test (3.13, lowest-direct, ubuntu-latest)	49s
checks / test (3.14, locked, ubuntu-latest)	2m 23s
checks / test (3.14, lowest-direct, windows-latest)	3m 4s
checks / test (3.14, locked, windows-latest)	4m 4s
checks / test (3.12, lowest-direct, windows-latest)	3m 46s
all-green	2s
	41m 54s

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