feat: add copy and paste using Ctrl+C/Ctrl+V

[Abrar74774]

What does this PR do?

This PR adds copy and paste (using Ctrl+C/Ctrl+V) functionality for singular nodes, rectangles and texts, as well as groups of them selected using the lasso select.

Fixes #115

Type of change

• Bug fix
• New feature
• Refactor (no functional change)
• Documentation update

Checklist

• I have read CONTRIBUTING.md
• I have tested these changes locally and they work
• I can explain every line of code in this PR if asked
• This PR does not contain AI-generated code that I haven't personally reviewed, understood, and tested
• I have not added any unnecessary comments, logging, or dead code
• My code follows the existing style and conventions of the project
• I have updated documentation if applicable

How to test

1. Select a node/text/rectangle by clicking on it, or select multiple of them using lasso select
2. Press Ctrl+C
3. Hover over the desired tile for pasting the item/item group
4. Press Ctrl+V

Each pasted item should retain their relative positioning if all the tiles are free, otherwise they'll be placed on the nearest unoccupied tile

Screenshots (if UI change)

No UI change since this PR only adds the copy/paste ability using hotkeys, although I plan to add context menus additions in another PR 🙂

[stan-smith]

@Abrar74774 what an absolute legend. Let me have a read through and then I'll merge this.
Thanks as always,
Stan