Add thread-safe `copy()`

[alippai]

Is your feature request related to a problem?

A new option for Dataset and DataArray .copy() function. Something between deep=True and deep=False.
#9836 here it was identified that everything in xarray is threadsafe, but the PandasIndex is not.

A shallow copy of the data, variables, coordinates + deep copy of the index is required for the fastest and most efficient thread-safe copy

Describe the solution you'd like

Add .copy(deep='threadsafe') or similar.

Describe alternatives you've considered

No response

Additional context

No response

[max-sixty]

I think this would be very difficult for xarray to guarantee — we'd be offering a contract on how what's threadsafe from each dependency...

reasonable as a user function or something in extras

but ofc open-minded!

[alippai]

You are right that the threading word is confusing. Maybe just an array like deep=[data, cords, index, attrs]?

[max-sixty]

I would mildly vote against it given that it expands the API without providing much broad value.

I'm on your side about the underlying issue being frustrating. but users who want this can write it / we could put it into https://xarray-extras.readthedocs.io/en/latest/...