Add unit tests for sidecar set annotation parsing

[GautamBytes]

This PR introduces comprehensive unit tests for the GetPodHotUpgradeInfoInAnnotations function in pkg/cmd/util/sidecar_set.go.

Reason for Change:

The GetPodHotUpgradeInfoInAnnotations function contains critical logic for parsing pod annotations, including JSON unmarshalling and handling missing data. Adding unit tests is essential to verify this logic, prevent future regressions, and improve the overall stability of the utility.

Testing Scenarios Covered:

The new test suite validates the function's behavior across multiple scenarios:

• A pod with a valid, well-formed JSON annotation.
• A pod that is missing the target annotation.
• A pod with a nil or empty annotations map.
• A pod where the annotation value contains invalid or malformed JSON.

These tests ensure the function is robust and handles both expected and edge-case inputs gracefully.

[kruise-bot]

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