Replace imghdr by puremagic

[bernt-matthias]

imghdr allowed to detect a few image types and has been deprecated in python 3.13

from the release notes:

The filetype, puremagic, or python-magic libraries should be used as replacements.
For example, the puremagic.what() function can be used to replace the imghdr.what()
function for all file formats that were supported by imghdr.

See also code comment

Since we do not really know how often PIL fails nowadays, we could also drop it. Overall I could imagine that puremagic could help us as well for the datatype sniffing (I think over there we reinvent the wheel from time to time).
The number of supported filetypes and being python only seems also in favor of puremagic (compared to filetype and python-magic)

Stumbled over this here: galaxyproject/bioblend#472

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[bernt-matthias]

Also dropping the import (as in #18449) at all would be fine for me (was also my first idea). Maybe we can split this out in a separate PR?

I did a few experiments with puremagic (for the sniffers for binary formats) ... which were not really promising (i.e. mostly false negatives).

[nsoranzo]

Not an expert in this, I am happy to backport my commit dropping imghdr if puremagic isn't that useful.
puremagic is still another requirement that we would need to add to the util package requirement, as you can see from the failing package tests, so we may be better off with pillow any way.

[jmchilton]

We only seem to use image_util from lib/galaxy/datatypes/images.py - it should probably be moved to galaxy-data - where the requirements make a lot more sense also.

[nsoranzo]

We only seem to use image_util from lib/galaxy/datatypes/images.py - it should probably be moved to galaxy-data - where the requirements make a lot more sense also.

I did try that, but image_util is also used to define the check_image() function in lib/galaxy/util/checkers.py , which in turn is used in lib/galaxy/datatypes/ (so fine) but also in lib/galaxy/tool_shed/util/tool_util.py, lib/galaxy/tool_util/loader_directory.py and lib/tool_shed/util/commit_util.py .

[bernt-matthias]

It has been in datatypes until 2016 #3042