Propagate contextvars through anyio streams #669

Job	Run time
checks / pre-commit	48s
checks / readme-snippets	10s
checks / test (3.10, locked, ubuntu-latest)	46s
checks / test (3.10, lowest-direct, ubuntu-latest)	57s
checks / test (3.11, locked, windows-latest)	2m 20s
checks / test (3.11, locked, ubuntu-latest)	50s
checks / test (3.10, locked, windows-latest)	2m 25s
checks / test (3.10, lowest-direct, windows-latest)	2m 46s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 5s
checks / test (3.13, lowest-direct, ubuntu-latest)	53s
checks / test (3.12, locked, windows-latest)	3m 22s
checks / test (3.12, locked, ubuntu-latest)	55s
checks / test (3.11, lowest-direct, ubuntu-latest)	52s
checks / test (3.12, lowest-direct, windows-latest)	3m 37s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 18s
checks / test (3.13, locked, windows-latest)	2m 15s
checks / test (3.11, lowest-direct, windows-latest)	2m 45s
checks / test (3.14, locked, ubuntu-latest)	2m 20s
checks / test (3.14, locked, windows-latest)	3m 7s
checks / test (3.13, lowest-direct, windows-latest)	2m 32s
checks / test (3.13, locked, ubuntu-latest)	48s
checks / test (3.14, lowest-direct, windows-latest)	3m 9s
all-green	4s
	40m 4s

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