Add `streamable_http_client` which accepts `httpx.AsyncClient` instead of `httpx_client_factory` #2901

Job	Run time
checks / pre-commit	29s
checks / readme-snippets	10s
checks / test (3.10, lowest-direct, ubuntu-latest)	34s
checks / test (3.10, highest, windows-latest)	1m 46s
checks / test (3.11, lowest-direct, windows-latest)	1m 27s
checks / test (3.10, highest, ubuntu-latest)	34s
checks / test (3.11, highest, ubuntu-latest)	33s
checks / test (3.10, lowest-direct, windows-latest)	1m 33s
checks / test (3.12, highest, windows-latest)	1m 29s
checks / test (3.13, highest, windows-latest)	1m 26s
checks / test (3.11, lowest-direct, ubuntu-latest)	33s
checks / test (3.11, highest, windows-latest)	1m 33s
checks / test (3.13, lowest-direct, windows-latest)	1m 39s
checks / test (3.13, lowest-direct, ubuntu-latest)	33s
checks / test (3.12, highest, ubuntu-latest)	33s
checks / test (3.12, lowest-direct, ubuntu-latest)	35s
checks / test (3.12, lowest-direct, windows-latest)	1m 27s
checks / test (3.13, highest, ubuntu-latest)	36s
	17m 30s

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