metis: Implement CNI Mode for Metis and Add Conformance Tests

[arvindbr8]

This PR implements the CNI (Container Network Interface) mode for the metis binary, enabling it to act as a gRPC client that communicates with the Metis daemon for dynamic pod IP allocation and deallocation over a Unix Domain Socket.

It also implements the CNI CHECK command properly by expanding the gRPC API to verify active locks against the SQLite backend.

Changes

1. CNI Plugin Implementation (cmd/)

• cmd/cni.go: Implemented cmdAdd, cmdDel, and cmdCheck utilizing the official skel package.
• Integrated the plugin as the default execution block in cmd/main.go when no subcommands are supplied.

2. Protocol Expansion for cmdCHECK

• adaptiveipam.proto: Added CheckPodIP RPC endpoint to poll state.
• daemon_server.go: Implemented the gRPC server handler for CheckPodIP.
• store.go: Added CheckAllocation to run targeted SQLite queries checking whether an edge still maps perfectly to a living container ID.

3. Tests

• cmd/cni_test.go:
  • Added unit tests mocking the gRPC clients.
  • Added an integration test that spins up a real daemon in a goroutine and verifies full lifecycle communication on a dummy socket.
• cmd/cni_conformance_test.go: Added a test suite utilizing the upstream CNI libcni package. This compiles our local CNI on-the-fly and acts exactly as containerd/kubelet would do, verifying full payload compliance.

Verification Results

Ran tests locally via isolated module workspace tags: GOWORK=off go test -v ./cmd

Output:

=== RUN   TestCmdAdd
--- PASS: TestCmdAdd (0.00s)
=== RUN   TestCmdDel
--- PASS: TestCmdDel (0.00s)
=== RUN   TestCmdCheck
--- PASS: TestCmdCheck (0.00s)
=== RUN   TestCniWithActualDaemon
--- PASS: TestCniWithActualDaemon (0.11s)
=== RUN   TestLibcniConformance
--- PASS: TestLibcniConformance (2.60s)
PASS
ok      k8s.io/metis/cmd        2.735s

All modules pass cleanly, and GitHub CI will automatically pick up these new test files upon pushing!

/hold for reviews from @YifeiZhuang @gnossen
/label tide/merge-method-squash

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: arvindbr8
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[arvindbr8]

/hold for reviews from @YifeiZhuang @gnossen
/label tide/merge-method-squash

[YifeiZhuang]

/ok-to-test