WIP: Implement partial reading for ISMRMRD files

[tknopp]

This is a first attempt to implement partial reading from ISMRMRD files (closes #76).
What is still missing is the fix of the header. I do not yet have an idea how to do that. We probably want to allow just UnitRanges for the applied slice argument.

@mrikasper @alexjaffray: I don't have data with multiple slices / repetitions at hand. Would be great if you could give this a test + help me fixing the header. The test should include timing. I expect that the sliced reading should be faster and acquire only the memory required for the slice. But I am only 90% sure about that.

[codecov-commenter]

Codecov Report

Base: 64.23% // Head: 64.23% // No change to project coverage 👍

Coverage data is based on head (011bd8a) compared to base (dcf7799).
Patch has no changes to coverable lines.

Additional details and impacted files

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  Coverage   64.23%   64.23%           
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  Files          37       37           
  Lines        1675     1675           
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  Hits         1076     1076           
  Misses        599      599           

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[alexjaffray]

Thanks for looping me in @tknopp. @mrikasper and I have spiral data available at https://zenodo.org/record/6510021#.Yxe_7y0r1QI and are just thinking about how to package it into a small, test-friendly example. I'l take a look at this branch and see what we need to do to make it work with our dataset.

[tknopp]

For the unit tests we could alternatively simulate some ISMRMRD files with our internal simulation framework. This would be more flexible.

[tknopp]

committed directly in 2e29cb9 since this had conflicts.