feat: add an api to get a sub-graph #644

Job	Run time
macos (macos-14, aarch64, 3.12)	1m 55s
linux (ubuntu-22.04, x86_64)	5m 31s
macos (macos-14, aarch64, 3.13)	1m 42s
macos (macos-14, aarch64, 3.11)	2m 21s
sdist	29s
Build wheel on ${{ matrix.platform.name }}	0s
	11m 58s

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