fix(ui): validate edges on paste

[psychedelicious]

Summary

Add validation when pasting edges. Uses the same validation logic as normal edge connections. A warning is logged if a pasted edge is invalid.

Related Issues / Discussions

Closes #7058

QA Instructions

Try the simple test cases:

• Copy & paste a source node and edge from the source node to a target node. The target field should only accept single connections.
• Copy & paste a source node and edge from the source node to a target node. The target field should accept multiple connections.

Video demonstrating the test cases: https://github.com/user-attachments/assets/831c7d73-fa1d-483a-977c-8b3834e428e2

Merge Plan

n/a

Checklist

• [x] The PR has a short but descriptive title, suitable for a changelog
• [ ] Tests added / updated (if applicable)
• [ ] Documentation added / updated (if applicable)