oci-worker: separate windows and linux oci worker code #10

Job	Run time
prepare	1s
test / prepare	1m 51s
test / run (containerd, ./frontend/dockerfile, integration)	4m 33s
test / run (containerd, ./frontend/dockerfile, dockerfile)	6m 52s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	4m 34s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	6m 49s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	5m 18s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	6m 20s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 43s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	8m 8s
test / run (oci, ./frontend/dockerfile, integration)	4m 2s
test / run (oci, ./frontend/dockerfile, dockerfile)	5m 30s
test / run (oci-rootless, ./frontend/dockerfile, integration)	4m 52s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	5m 9s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	4m 3s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	5m 19s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 7s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	5m 54s
image (mainline)	4m 53s
image (labs)	4m 56s
release	0s
	1h 38m 54s

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