Propagate contextvars through anyio streams #658

Job	Run time
checks / readme-snippets	16s
checks / pre-commit	31s
checks / test (3.10, lowest-direct, windows-latest)	2m 31s
checks / test (3.10, lowest-direct, ubuntu-latest)	46s
checks / test (3.10, locked, windows-latest)	3m 18s
checks / test (3.11, lowest-direct, windows-latest)	2m 42s
checks / test (3.10, locked, ubuntu-latest)	52s
checks / test (3.12, locked, ubuntu-latest)	56s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.13, lowest-direct, ubuntu-latest)	44s
checks / test (3.12, locked, windows-latest)	3m 21s
checks / test (3.13, locked, windows-latest)	2m 31s
checks / test (3.11, lowest-direct, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, windows-latest)	3m 26s
checks / test (3.11, locked, windows-latest)	2m 42s
checks / test (3.12, lowest-direct, ubuntu-latest)	46s
checks / test (3.14, locked, windows-latest)	3m 14s
checks / test (3.13, locked, ubuntu-latest)	44s
checks / test (3.13, lowest-direct, windows-latest)	2m 50s
checks / test (3.14, lowest-direct, windows-latest)	2m 40s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 10s
checks / test (3.14, locked, ubuntu-latest)	2m 18s
all-green	4s
	40m 1s

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