forkexec: fix unshare cgroup with ptracer

mount: allow read write mount for /proc

criyle/go-judge#106

Co-authored-by: iBug <[email protected]>

container: add option to run init command after container initialization

deps: upgrade to rand/v2

cgroup: rename types to remove stutters

cgroup: refactor to support creating child cgroup directly

deps: upgrade to go1.21

doc: update kernel version doc and dependency versions

*: bump dependency version & better align

*: bump dependency version with go1.20