Feat: display Node, Topic counts in ROS domain

[nshro]

Overview

This PR enhances the RosEntityListPanel widget to display element counts in the tree view, providing better visibility into the number of ROS entities at each level of the hierarchy.

Highlights

• Top-level count display: Root nodes (e.g., "Node", "Topic") now show the total count of all entities in parentheses
• Group-level count display: Each group node displays the count of its direct child elements
• Hierarchical counting: Counts are calculated independently at each level without including parent counts

Notes

• The counting logic distinguishes between total counts (for root nodes) and group-specific counts (for group nodes)

Node (6)
├── group1 (3)
│   ├── child1
│   ├── child2
│   └── child3
├── group2 (2)
│   ├── child4
│   └── child5
└── group3 (1)
    └── child6

[Copilot]

Pull Request Overview

This PR adds count indicators to the ROS entity tree view, showing the total number of entities at the root level and individual counts for each group. The implementation calculates counts for grouped entities and displays them in parentheses next to node labels.

• Adds display of total entity count at root level (e.g., "Node (6)")
• Shows group-specific counts for each group node (e.g., "group1 (3)")
• Implements counting logic using dictionaries to track entities per group

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[Tiryoh]

LGTM!