Mrcfile

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* Fix rare bug in mmap alignment with certain extended header sizes
* Add test and documentation code to source distribution
* Add support for Python 3.13 and numpy 2.1 & 2.2

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* Fix opening of large files in numpy 2.0 (in general this time, not just for
mmap)
* Raise errors if data or extended header arrays are too large for their
dimensions to be stored in the header
* Validate header statistics only if they are set

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* Fix opening of very large files with mmap in numpy 2.0 (thanks to Hanjin
Liu)

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* Add support for numpy 2.0

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* Add new 'indexed_extended_header' attribute to access the indexed part of
the extended header if it exists (thanks to David Waterman). Note that this
introduces a change in behaviour: code that used the 'extended_header'
attribute directly to access items in FEI1- and FEI2-type extended headers
will need to be updated to use 'indexed_extended_header' instead.
* Add support for numpy 1.24, 1.25 and 1.26 and Python 3.12