Add unit tests for historyViewer

[GautamBytes]

This PR introduces two small indirection hooks in historyviewer.go - coreNewForConfig and kruiseNewForConfig - that default to the real Kubernetes and Kruise client constructors. By doing so we can inject failures in unit tests without altering any production behavior.

Additionally, it adds a new test file historyviewer_test.go which achieves 100% coverage of the historyViewer function’s error paths:

• RESTConfig failure: ensures an error from ToRESTConfig is propagated unchanged.
• Kubernetes client construction failure: simulates NewForConfig returning an error (“core fail”).
• Kruise client construction failure: simulates NewForConfig returning an error (“kruise fail”).

[kruise-bot]

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