Adds logic to handle isolated vertices at python layer #3041

Job	Run time
checks / other-checks	51s
checks / check-style	3m 5s
wheel-build-pylibcugraph / compute-matrix	4s
conda-cpp-build / compute-matrix	3s
conda-cpp-build / build (11.8.0, ubuntu22.04, amd64, 3.10)	26m 45s
conda-cpp-build / build (11.8.0, ubuntu22.04, arm64, 3.10)	25m 44s
conda-cpp-build / build (12.0.1, ubuntu22.04, amd64, 3.10)	24m 55s
wheel-build-pylibcugraph / 11.8.0, 3.9, amd64, centos7	12m 58s
wheel-build-pylibcugraph / 11.8.0, 3.10, amd64, centos7	12m 53s
wheel-build-pylibcugraph / 11.8.0, 3.9, arm64, ubuntu20.04	9m 15s
wheel-build-pylibcugraph / 11.8.0, 3.10, arm64, ubuntu20.04	9m 16s
wheel-build-pylibcugraph / 12.0.1, 3.9, amd64, centos7	12m 48s
wheel-build-pylibcugraph / 12.0.1, 3.10, amd64, centos7	12m 50s
wheel-build-pylibcugraph / 12.0.1, 3.9, arm64, ubuntu20.04	9m 38s
wheel-build-pylibcugraph / 12.0.1, 3.10, arm64, ubuntu20.04	9m 32s
wheel-tests-pylibcugraph / compute-matrix	4s
wheel-tests-pylibcugraph / 11.8.0, 3.9, amd64, ubuntu18.04, v100	1s
wheel-tests-pylibcugraph / 12.0.1, 3.10, amd64, ubuntu18.04, v100	1s
wheel-tests-pylibcugraph / 12.0.1, 3.9, arm64, ubuntu20.04, a100	9m 23s
wheel-build-cugraph	1s
wheel-tests-cugraph	1s
conda-cpp-tests	1s
conda-python-build	1s
docs-build	1s
conda-python-tests	1s
conda-notebook-tests	1s
pr-builder	1s
	3h 0m 14s

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