Move set_nan_defaults to be a stand-alone function

[dachengx]

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What does the code in this PR do / what does it improve?

Depends on AxFoundation/strax#936

Close: #1491

Can you briefly describe how it works?

Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Notes on testing

• Until the automated tests pass, please mark the PR as a draft.
• On the XENONnT fork we test with database access, on private forks there is no database access for security considerations.

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[coveralls]

coverage: 89.491% (+0.01%) from 89.48%
when pulling 7ac39f8 on move_set_nan_defaults
into f765c10 on master.