fix(cubelet): register metric plugin to enable /v1/metrics/scheduler endpoint

[chenggui53]

The metric plugin was missing from builtins.go, so its init() never ran and the /v1/metrics/scheduler endpoint returned 404. Adding the blank import so the plugin registers with containerd's plugin system.

[kinwin-ustc]

/cubebot review

[github-actions]

Claude finished @kinwin-ustc's task in 44s —— View job

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Code Review

Summary

This PR adds a blank import for the metric plugin (Cubelet/plugins/cube/internals/metric) in builtins.go. Without this import, the plugin's init() function never executes, and containerd's plugin system never registers the metric service, causing the /v1/metrics/scheduler endpoint to return 404.

What was checked

• Diff correctness: The added import is in alphabetical order within the cube/internals/* import block — it's correctly placed between cubes and netfile.
• Plugin registration: The metric plugin (plugin.go line 44) uses registry.Register() in its init(), so a blank import is the correct and sufficient mechanism to trigger registration.
• Pattern consistency: This follows the same convention as all other plugins in the file (e.g., sandbox, cgroup, createid, images, etc.).

Finding

LGTM — the change is correct and minimal. The single-line addition is exactly what's needed. No issues found.

Minor note (pre-existing, not related to this PR)

There's a duplicate import of cube/multimeta at lines 69 and 74. This is unrelated to the fix here, but worth cleaning up in a follow-up since duplicate imports are a dead code smell.

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• Read the diff
• Verified the metric plugin uses init() + registry.Register()
• Confirmed alphabetical placement within import block
• Reviewed for correctness and completeness