⚡ Bolt: [performance improvement] Cache expensive UI options in ScenarioEditorViewModel

[google-labs-jules]

💡 What:
Updated ScenarioEditorViewModel to cache the results of NodeIdOptions, EdgeIdOptions, and TrafficTypeOptions in private nullable backing fields instead of recalculating them on every property getter access. Added cache invalidation (= null) in RaiseReferenceDataChanged().

🎯 Why:
Previously, these properties were expression-bodied members evaluating a full LINQ chain (.Select().OrderBy().ToList()) on every access. In Avalonia/WPF applications, property getters can be accessed extremely frequently during UI data-binding layout passes and value change propagations. This caused severe, unnecessary allocations, object creation, string sorting overhead, and garbage collection pressure every single time the UI simply asked for the drop-down options.

📊 Impact:
Eliminates hundreds of redundant List<string> allocations and $O(N \log N)$ string sorting operations per network interaction, reducing garbage generation and CPU spikes when ScenarioEditorViewModel is bound to the view.

🔬 Measurement:
No new logic was introduced. Unit tests pass locally. Verified that RaiseReferenceDataChanged() is correctly hooked up to invalidate the cache.

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PR created automatically by Jules for task 7346833513431176838 started by @wnj00524

[google-labs-jules]

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