Feat: added pop message to shrinkingmap

[hmoog]

Description of change

Thir PR adds a convenience function for the ShrinkingMap, that allows to Pop the first element.

Type of change

• Enhancement (a non-breaking change which adds functionality)

Change checklist

• My code follows the contribution guidelines for this project
• 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
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes