Optimize agent index

[joonyeol-sim]

Summary

This refactor replaces per-agent canvas item iteration with shared canvas tags for agent-related UI elements in PlanViz2024.

What changed

• Added dedicated canvas tag constants for:
  • dynamic agent objects
  • direction indicators
  • static/start objects
  • dynamic agent labels
  • static/start labels
• Added helper methods to tag agent canvas items and initialized tags during setup.
• Updated agent visibility/z-order logic to use bulk tag_raise and itemconfig operations on tags instead of looping through every agent.
• Ensured dynamically recreated direction items are re-tagged after redraw.

Why

Using tags centralizes agent canvas item management, simplifies the code path, and avoids repeated per-agent loops for common visibility and layering operations. Issues #63

Impact

• No intended functional behavior change.
• Improves maintainability and should scale better with larger agent counts.