Add `streamable_http_client` which accepts `httpx.AsyncClient` instead of `httpx_client_factory` #2812

Job	Run time
checks / pre-commit	34s
checks / readme-snippets	14s
checks / test (3.11, lowest-direct, windows-latest)	1m 23s
checks / test (3.10, lowest-direct, ubuntu-latest)	36s
checks / test (3.10, lowest-direct, windows-latest)	1m 20s
checks / test (3.11, lowest-direct, ubuntu-latest)	33s
checks / test (3.10, highest, ubuntu-latest)	33s
checks / test (3.10, highest, windows-latest)	1m 21s
checks / test (3.12, lowest-direct, windows-latest)	1m 31s
checks / test (3.11, highest, ubuntu-latest)	35s
checks / test (3.11, highest, windows-latest)	1m 45s
checks / test (3.12, lowest-direct, ubuntu-latest)	34s
checks / test (3.12, highest, ubuntu-latest)	36s
checks / test (3.13, lowest-direct, windows-latest)	5m 3s
checks / test (3.13, highest, ubuntu-latest)	36s
checks / test (3.12, highest, windows-latest)	1m 26s
checks / test (3.13, lowest-direct, ubuntu-latest)	36s
checks / test (3.13, highest, windows-latest)	1m 38s
	20m 54s

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