Fix task transform

[kkoehn]

fixes some not respected cases and edge cases

• When importing the xml and converting some data through dachsfisch it cannot be assume, that an Array is formed, when only one object is present in a list.

• external-resource did not get cleaned

• file-restriction attribute @use is not required

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (49216a4) to head (1c49eb9).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #409   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           35        35           
  Lines         1418      1487   +69     
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+ Hits          1418      1487   +69     

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[MrSerth]

I took a brief moment to validate the changes within the given domain: They look fine and valid. However, doing so was quite challenging for me, since I feel there is also no clear change log between ProFormA 2.0 and 2.1. Nevertheless, the code gave me enough information to dig through the schema files on my own and spot the differences.

Code-wise, I am leaving the review for @Dome-GER. I am unsure about potential improvements, this looks rather complex overall. Now, there seem some minor code duplicates (such as ensuring we have an array for external resources and submission restrictions)...