Library: Use multitrait handle

[iopapamanoglou]

Library: Use multitrait handle

Description

• Adapt multi traits: Descriptive; Picker; Linked Pad
• Move from add_trait to add
• Add checks to not allow instantiate raw trait

Fixes # (issue)

Checklist

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• My code follows the coding guidelines of this project
• My PR title is following the contribution guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I ran Black to format my code

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