limit memory usage of fwDicomIOFilterTest & fwDcmtkIOTest
Summary
fwDicomIOFilterTest & fwDcmtkIOTest use a huge amount of RAM when executing, this need to be reduced when running on CI.
Steps to reproduce
Launch fwDicomIOFilterTest & fwDcmtkIOTest.
Relevant logs and/or screenshots
From macos CI:
Possible fixes
Replace deepCopy by shallowCopy in fwDicomIOFilter