Tests

[ENH] Refactor `Extension` #1715

Job	Run time
(ubuntu-latest, Py3.8, sk0.23.1, sk-only:false)	3s
docker	3s
(windows-latest, Py, sk0.24.*, sk-only:false)	2s
(ubuntu-latest,Py3.10,sk1.4.*,sk-only:true)	44s
(ubuntu-latest,Py3.10,sk1.6.*,sk-only:true)	49s
(ubuntu-latest,Py3.11,sk1.3.*,sk-only:true)	41s
(ubuntu-latest,Py3.12,sk1.3.*,sk-only:true)	56s
(ubuntu-latest,Py3.11,sk1.5.*,sk-only:true)	1m 6s
(ubuntu-latest,Py3.10,sk1.7.*,sk-only:true)	44s
(ubuntu-latest,Py3.12,sk1.4.*,sk-only:true)	49s
(ubuntu-latest,Py3.11,sk1.6.*,sk-only:true)	48s
(ubuntu-latest,Py3.11,sk1.7.*,sk-only:true)	47s
(ubuntu-latest,Py3.10,sk1.5.*,sk-only:true)	46s
(ubuntu-latest,Py3.11,sk1.4.*,sk-only:true)	41s
(ubuntu-latest,Py3.12,sk1.5.*,sk-only:true)	45s
(ubuntu-latest,Py3.14,sk1.7.*,sk-only:true)	54s
(ubuntu-latest,Py3.12,sk1.7.*,sk-only:true)	57s
(ubuntu-latest,Py3.13,sk1.6.*,sk-only:true)	56s
(ubuntu-latest,Py3.14,sk1.5.*,sk-only:true)	4m 4s
(ubuntu-latest,Py3.13,sk1.5.*,sk-only:true)	48s
(ubuntu-latest,Py3.12,sk1.6.*,sk-only:true)	50s
(ubuntu-latest,Py3.13,sk1.7.*,sk-only:true)	47s
(ubuntu-latest,Py3.10,sk1.3.*,sk-only:true)	42s
(windows-latest,Py3.12,sk1.5.*,sk-only:false)	2m 0s
(ubuntu-latest,Py3.14,sk1.6.*,sk-only:true)	3m 58s
(ubuntu-latest,Py3.14,sk1.7.*,sk-only:false)	59s
(ubuntu-latest,Py3.12,sk1.5.*,sk-only:false)	50s
	27m 29s

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