wrap recurring graph pattern as CuGraph helpers

[makeecat]

Summary

Identified the recurring patterns (BFS traversal, edge iteration, edge-id lookup) and surfaced them as CuGraph helpers, then refactored runtime/monitoring/derive to consume the new API so petgraph stays internal.

address issue: #335

Details

• Added CuGraph traversal/edge helpers (node_ids, edges, edge, edge_id_between, bfs_nodes) in core/cu29_runtime/src/config.rs to cover the patterns without exposing petgraph types.
• Swapped runtime planning over to the new helpers (BFS traversal, edge lookup, neighbor enqueueing) in core/cu29_runtime/src/curuntime.rs.
• Updated monitoring and codegen to iterate connections via graph.edges() instead of petgraph iterators in core/cu29_runtime/src/monitoring.rs and core/cu29_derive/src/lib.rs.

[makeecat]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

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[gbin]

OMG this is SO much better