Propagate contextvars.Context through anyio streams without modifying SessionMessage #1724

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	36s
checks / test (3.11, locked, windows-latest)	3m 5s
checks / test (3.13, locked, ubuntu-latest)	44s
checks / test (3.12, locked, ubuntu-latest)	57s
checks / test (3.13, locked, windows-latest)	2m 8s
checks / test (3.12, locked, windows-latest)	3m 7s
checks / test (3.14, lowest-direct, windows-latest)	2m 39s
checks / test (3.10, lowest-direct, ubuntu-latest)	51s
checks / test (3.12, lowest-direct, windows-latest)	3m 51s
checks / test (3.10, locked, ubuntu-latest)	50s
checks / test (3.13, lowest-direct, ubuntu-latest)	51s
checks / test (3.12, lowest-direct, ubuntu-latest)	59s
checks / test (3.10, lowest-direct, windows-latest)	2m 45s
checks / test (3.11, lowest-direct, windows-latest)	2m 29s
checks / test (3.14, locked, windows-latest)	3m 3s
checks / test (3.13, lowest-direct, windows-latest)	2m 48s
checks / test (3.11, locked, ubuntu-latest)	50s
checks / test (3.11, lowest-direct, ubuntu-latest)	51s
checks / test (3.10, locked, windows-latest)	2m 5s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.14, locked, ubuntu-latest)	2m 15s
all-green	3s
	39m 11s

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