fix: avoid taint cleanup for dry-run rules (#374)

[alanhuangch]

Description

Prevent deleting an always-dry-run NodeReadinessRule from removing pre-existing Node taints. The cleanup finalizer is now added only when a rule enters enforcement and is retained across later transitions back to dry-run.

Related Issue

Fixes #374

Type of Change

/kind bug

Testing

• make test passes (including controller-gen, gofmt, go vet, and all non-e2e tests; controller suite 64/64)
• make lint passes (golangci-lint and kube-api-linter)

Checklist

• make test passes
• make lint passes

Does this PR introduce a user-facing change?

Yes: deleting a rule that remained in dry-run mode no longer mutates Node taints.

Deleting an always-dry-run NodeReadinessRule no longer removes matching pre-existing Node taints.

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[kubernetes-prow]

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[kubernetes-prow]

Hi @alanhuangch. Thanks for your PR.

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[ajaysundark]

/ok-to-test

[ajaysundark]

I understand the rationale here, but wouldnt a 'stuck' taint has more side effects than cleaning it up? From a safety standpoint, erring on the side of cleaning up taints might be preferable.

Even in a scenario where a user deletes a dry-run rule to update and reapply it, NRC would re-add missing taints to enforce readiness anyway. Could you clarify where do you see leaving the taints is preferred here?