feat: handle singularity/apptainer sandbox images

[natthan-pigoux]

Running cwltool with dockerRequirements (with pull disabled) using a local Singularity/Apptainer sandbox image is not currently handle. cwltool is only searching for files (e.g. sif images) and not path as it should for sandbox images.

Here I provide:

• a function using singularity inspect to verify that a path is a singularity image
• searching for the sandbox image in the get_image method
• a test which build an alpine sandbox image and use it in dockerPull

Some questions I have:

• if the sandbox image is found I decided to skip the candidates search, I don't know if we wish that
• I'm not sure the singularity inspect is strong enough to ensure the presence of the image

It is the first time I contribute here so I might have miss some things :)

closes #2165

[codecov]

Codecov Report

❌ Patch coverage is 34.78261% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.44%. Comparing base (766d58b) to head (ca94aa0).

Files with missing lines	Patch %	Lines
cwltool/singularity.py	34.78%	15 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (766d58b) and HEAD (ca94aa0). Click for more details.

HEAD has 5 uploads less than BASE

Flag	BASE (766d58b)	HEAD (ca94aa0)
	17	12

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2166      +/-   ##
==========================================
- Coverage   85.10%   77.44%   -7.66%     
==========================================
  Files          46       46              
  Lines        8358     8380      +22     
  Branches     1951     1955       +4     
==========================================
- Hits         7113     6490     -623     
- Misses        779     1370     +591     
- Partials      466      520      +54     

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[mr-c]

Thank you @natthan-pigoux ; can you run make cleanup and push again?

[natthan-pigoux]

@mr-c , thank you to already have a look. I will be away next week, so I will probably not answer before 2nd November.

[natthan-pigoux]

@mr-c , sorry I should have put this PR as Draft before ... but now it should be ready for review. The tests should cover quiet well the changes.