libcgroups v2 manager stats doesn't set cpu throttling field

[Sherlock Holo]

youki/crates/libcgroups/src/v2/cpu.rs

Line 65 in 77d3166

 fn stats(cgroup_path: &Path) -> Result<Self::Stats, Self::Error> { 

we can see the v2 manager stats doesn't set cpu throttling field, user can't get the cpu.max data when using v2 manager

[Toru Komatsu]

@Sherlock-Holo Thanks for your report. May I ask you to contribute?