`user.slice` path must not be hardcoded (affects WSL2.9)

[AkihiroSuda]

nerdctl/pkg/infoutil/infoutil_linux.go

Line 144 in 833c457

g := fmt.Sprintf("/user.slice/user-%d.slice", rootlessutil.ParentEUID())

nerdctl/pkg/cmd/container/run_cgroup_linux.go

Line 238 in 833c457

slice = "user.slice"

nerdctl/extras/rootless/containerd-rootless-setuptool.sh

Line 115 in 833c457

controllers="/sys/fs/cgroup/user.slice/user-${id}.slice/user@${id}.service/cgroup.controllers"

The cgroup path must not be hardcoded, as the path may differ on WSL2 since WSL2.9.

• [WSL 2.9 regression] Rootless Docker/Podman cannot start any container — standard /sys/fs/cgroup/user.slice path missing after cgroup hierarchy moved under /wsl-user/distro-N/ microsoft/WSL#41492
• Rootless dockerd assumes user.slice is at the cgroup v2 root, breaking under nested systemd cgroup hierarchies (e.g., on WSL 2.9) moby/moby#53531
• Implement dynamic cgroup detection moby/moby#53533

Help wanted from WSL2 users.