Adopt ~Copyable in `Subprocess` #18

Job	Run time
Test / Windows (6.1 - windows-2022)	19m 31s
Test / Linux (6.1 - noble)	50s
Test / Windows (nightly-main - windows-2019)	9m 3s
Test / Linux (6.1 - jammy)	49s
Test / Linux (6.1 - focal)	48s
Test / macOS (Xcode 16.3 - sequoia - ARM64)	41s
Test / Linux (6.1 - rhel-ubi9)	56s
Test / Linux (nightly-main - noble)	1m 2s
Test / Linux (nightly-main - jammy)	1m 4s
Test / Linux (nightly-main - focal)	1m 2s
Test / Linux (nightly-main - rhel-ubi9)	1m 17s
Soundness / API breakage check	0s
Soundness / Documentation check	0s
Soundness / Broken symlinks check	5s
Soundness / Format check	0s
Soundness / License headers check	5s
Soundness / Python lint check	6s
Soundness / Shell check	38s
Soundness / Unacceptable language check	0s
Soundness / YAML lint check	2s
	37m 59s

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