chore: Backport NillableDuration updates for v0.37.x

[rschalo]

Fixes #N/A

Description

• Backporting: fix: ensure NillableDuration is round-trippable #1545

How was this change tested?
make presubmit

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[k8s-ci-robot]

Hi @rschalo. Thanks for your PR.

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[jonathan-innis]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jonathan-innis, rschalo

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