Add `streamable_http_client` which accepts `httpx.AsyncClient` instea… #523

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	31s
checks / test (3.12, lowest-direct, ubuntu-latest)	53s
checks / test (3.11, lowest-direct, windows-latest)	2m 22s
checks / test (3.11, highest, windows-latest)	2m 42s
checks / test (3.10, highest, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, windows-latest)	2m 18s
checks / test (3.12, highest, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, ubuntu-latest)	48s
checks / test (3.11, highest, ubuntu-latest)	47s
checks / test (3.12, highest, windows-latest)	3m 34s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.13, highest, windows-latest)	2m 35s
checks / test (3.12, lowest-direct, windows-latest)	3m 18s
checks / test (3.13, highest, ubuntu-latest)	48s
checks / test (3.10, highest, windows-latest)	2m 30s
checks / test (3.13, lowest-direct, windows-latest)	2m 29s
checks / test (3.13, lowest-direct, ubuntu-latest)	50s
	29m 7s

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