bug fix: NaN observables

[lanther]

What does this PR do?

observables shouldn't trigger a change if a NaN is changed to a NaN. Issue is that NaN !== NaN in JS, so need an additional check for this case.

Checklist

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• [ ] An issue has been created for this PR
• [ ] Title begins with one of the following: Fix:, Update:, Breaking:, or New:
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• [ ] PR includes new unit tests as necessary (or will be submitted as a separate PR)
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