Propagate contextvars.Context through anyio streams without modifying SessionMessage #1723

Job	Run time
checks / pre-commit	34s
checks / readme-snippets	16s
checks / test (3.11, lowest-direct, ubuntu-latest)	54s
checks / test (3.11, locked, windows-latest)	2m 6s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.11, locked, ubuntu-latest)	46s
checks / test (3.10, lowest-direct, ubuntu-latest)	59s
checks / test (3.12, lowest-direct, windows-latest)	4m 2s
checks / test (3.10, locked, windows-latest)	2m 10s
checks / test (3.13, lowest-direct, windows-latest)	2m 25s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 17s
checks / test (3.13, lowest-direct, ubuntu-latest)	58s
checks / test (3.14, lowest-direct, windows-latest)	2m 1s
checks / test (3.10, lowest-direct, windows-latest)	2m 24s
checks / test (3.13, locked, windows-latest)	2m 17s
checks / test (3.13, locked, ubuntu-latest)	49s
checks / test (3.14, locked, windows-latest)	3m 18s
checks / test (3.14, locked, ubuntu-latest)	2m 20s
checks / test (3.12, locked, windows-latest)	3m 40s
checks / test (3.12, locked, ubuntu-latest)	52s
checks / test (3.11, lowest-direct, windows-latest)	2m 15s
checks / test (3.10, locked, ubuntu-latest)	53s
all-green	5s
	38m 21s

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