Support external kernels #2207

Job	Run time
build (ubuntu-latest, 3.8)	2m 30s
build (ubuntu-latest, 3.11)	2m 26s
build (windows-latest, 3.8)	2m 2s
build (windows-latest, 3.11)	2m 2s
build (macos-latest, 3.8)	52s
build (macos-latest, 3.11)	46s
build (windows-latest, 3.9)	2m 26s
build (ubuntu-latest, pypy-3.8)	2m 22s
build (macos-latest, 3.10)	52s
build (ubuntu-latest, 3.12)	2m 7s
Test Docs	43s
Test Examples	43s
Test Lint	31s
Test Minimum Versions	46s
Check Links	3m 1s
check_release	35s
integration_check (ubuntu-latest, 3.8)	27s
integration_check (ubuntu-latest, 3.9)	25s
integration_check (ubuntu-latest, 3.10)	27s
integration_check (ubuntu-latest, 3.11)	40s
integration_check_pypy	47s
Make SDist	38s
Test Prereleases	52s
Install from SDist and Test	0s
coverage	0s
tests_check	3s
	29m 3s

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