Summary

This PR adds a caching mechanism for the DAG (Directed Acyclic Graph) layout in the console monitor to improve scrolling performance. Previously, the graph was rebuilt on every render frame; now it's cached and only rebuilt when necessary (on resize or graph structure changes).

Related Issue: #683

Details

Changes in cu_consolemon/src/lib.rs

New caching infrastructure:

• Added GraphCacheKey struct (lines 375-380) to track cache validity based on area size, node
  count, and connection count
• Added GraphCache struct (lines 382-405) to store the computed NodeGraph, content size, and cache
  key
• Added needs_rebuild() method to determine when cache invalidation is needed

Refactored NodesScrollableWidgetState:

• Moved graph building logic from StatefulWidget::render() into state methods:
  • ensure_graph_cache() - lazily initializes/rebuilds cache as needed
  • rebuild_graph_cache() - performs actual graph computation and layout
  • build_graph() / build_node_layouts() - extracted helper methods
  • clamp_scroll_offset() - ensures scroll position stays within bounds
  • mark_graph_dirty() - called on window resize to force rebuild

Simplified render method:

• NodesScrollableWidget::render() now simply calls state.ensure_graph_cache(area) and uses the cached graph
• Removed the inline GraphWrapper struct (now uses &NodeGraph directly)
• Minor code cleanups: simplified index clamping, extracted repeated node variable

Resize handling:

• Added mark_graph_dirty() call on Event::Resize to invalidate cache when terminal size changes

Changes in cu_consolemon/src/tui_nodes/graph.rs

• Extracted render logic into render_into(&self, ...) method to allow rendering from a reference
• Changed node iteration from into_iter() to iter() to avoid consuming the graph
• Added Widget impl for &'a NodeGraph<'a> (lines 420-424) enabling the graph to be rendered by reference