Niondata

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- Add power function (xdata.power).
- Add radial profile function (xdata.radial_profile).
- Improve handing of invalid inverse coordinates (1/0).
- Add support for computing the phase of a complex array (thanks Luc J Bourhis).
- Improve performance (eliminate some unnecessary metadata dict copying)

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- Minor update for typing compatibility.

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- Reapply DataMetadata read-only accessors change.
- Make read-only accessors to all DataMetadata properties instead of having them be read/write.

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- Revert breaking change: DataMetadata read-only accessors.

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- Introduce rebin_factor xdata function.
- Carry through intensity calibration during FFT/IFFT.
- Add copy magic method to data metadata.
- Make read-only accessors to all DataMetadata properties instead of having them be read/write.
- Require Python 3.9 or higher.

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- Add is_valid method to calibrations and use when converting to strings.