Compression options for saving output.

[YooSunYoung]

NMXReducedData keeps pixel id coordinate and there are >1e6 pixels
so it could carry relatively large data (>GB) in the end.

Therefore we would like to compress the large-size Dataset when we save it into h5 or nexus file.
The compression option is now hard-coded, but it makes saving very slow.
Some advanced users, i.e. IDS might want to turn it off when they have to debug the workflow.

Therefore we should

• Find the optimal compression options comparing the advantages between speed and size of the output.
• Make it possible to lower the compression option, with the optimal compression by default.
• Document about compression in the workflow user-guide.

[SimonHeybrock]

HDF5 compression / decompression is really slow. We should imho never use it.

[YooSunYoung]

Hmm but @Justin-Bergmann requested to include this for saving the data.
Is there an alternative to reduce the size of the files...?

[SimonHeybrock]

Is the problem that this is stored for every wavelength slice?

How about storing all slices in the same file, then the pixels ids can be reused?

[YooSunYoung]

Is the problem that this is stored for every wavelength slice?

How about storing all slices in the same file, then the pixels ids can be reused?

I think we are already doing that.