Add more exception handlers to kubernetes config loading

[avnig05]

Hardens _is_kubernetes_installed_and_configured() in src/toil/test/init.py to gracefully handle invalid Kubernetes auth/config states. Adds explicit handling for oauthlib.oauth2.rfc6749.errors.CustomOAuth2Error when kube credentials are rejected by the cluster. Adds a broad safety catch for unexpected exceptions during config loading, logs context, and returns False so tests can skip Kubernetes-dependent paths cleanly.

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