fix(kubernetes): wait for PVC binding

[MarcStdt]

Summary

• treat immediate PVC provisioning as transient pod scheduling
• preserve immediate failure for genuinely unschedulable helper Pods
• prevent registry credentials from being cleaned up before a new PVC binds

Production evidence

A new helper Pod was marked failed after five seconds while its immediate-binding PVC was provisioning; the PVC became Bound moments later.

Validation

• GOCACHE=/tmp/druid-go-build go test ./internal/runtime/kubernetes

[druid-infra]

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