Improve code quality and test coverage of Item

[JaZo]

Description

I've split Item into several traits/concerns to group some logic together and make the class cleaner. All concerns have tests. Besides that, I added some missing tests for other classes as well.

I also renamed some methods to align all method names and make them less confusing. This is a (documented) breaking change.

Motivation and context

This should increase the code quality and test coverage of Item and some other classes.

How has this been tested?

Tested with new and updated unit tests.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply.

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.