[Feature Request]: Collapsible Visual Groups in Pipelines (Fold/Unfold Without Changing Execution)

### What would you like to happen?

Add a visual grouping capability in the Hop GUI to collapse a user-selected set of transforms and hops into a single Group Block. The group is purely diagrammatic: it does not change runtime behavior and does not create a sub-pipeline/mapping. Users can group, ungroup, and expand at any time to restore the full data flow view while keeping the original execution semantics intact.

Benefits

Improved readability for large pipelines (less visual sprawl).

Faster navigation and maintenance by working in logical sections (e.g., lookup/enrichment zone).

Reduced editing mistakes: clearer control over complex areas.

Better visual standardization for repeated patterns (e.g., “Lookup Enrichment”).

Pros

Low conceptual overhead: no refactoring and no new executable artifacts.

Complements mapping/subpipelines: ideal when you want organization, not reuse.

Helps onboarding: pipelines become easier to understand at a glance.

### Issue Priority

Priority: 3

### Issue Component

Component: Hop Gui

Start by reviewing the Hop GUI pipeline view and how transforms and hops are represented visually. Define how users select, group, ungroup, collapse, and expand those elements while keeping runtime execution unchanged. Done means the visual group can be edited or removed at any time and the original data flow remains intact.

Written by the indexing model from the issue text.