Support checkpoint in the containerd-shim

### Description

Hello gVisor maintainers,

It appears checkpointing isn’t implemented in the gVisor containerd-shim
https://github.com/google/gvisor/blob/2e9ad0022b4284e80eabc936c8dd2a27ab372de0/pkg/shim/v1/runsc/service.go#L612

#### Background
1. There is a previous issue #3275 (opened in 2020) requesting checkpoint/restore support.
2. PR #10623 seems to address parts of this, but checkpointing in the shim does not yet appear available.

#### Questions
1. Is there a timeline or plan to add checkpoint in the shim?
2. If implemented or in progress, can you point to the tracking issue/discussion?

### Is this feature related to a specific bug?

_No response_

### Do you have a specific solution in mind?

_No response_