Expose InteractiveViewer properties on GraphView.builder

[4rthurmonteiro]

Summary

• GraphView.builder wraps its content in an InteractiveViewer to provide pan/zoom, but its configuration (zoom limits, pan/scale enablement, interaction callbacks, etc.) was hardcoded. This PR exposes the most commonly used InteractiveViewer properties directly on GraphView.builder — clipBehavior, panAxis, boundaryMargin, minScale, maxScale, interactionEndFrictionCoefficient, onInteractionStart/Update/End, panEnabled, scaleEnabled, scaleFactor, alignment, and trackpadScrollCausesScale — so consumers can customize pan/zoom behavior without reaching into the widget tree.
• Defaults match the previous hardcoded values, so this is backward compatible.
• Converted several previously mutable GraphView fields (panAnimationDuration, toggleAnimationDuration, initialNode, autoZoomToFit, delegate) to final, since they were only ever set through the constructor.
• Updated Matrix4 transform calls (translate/scale) to their newer translateByDouble/scaleByDouble equivalents, and fixed Edge.operator== to take a non-nullable Object per the standard Object.== signature.
• Ran dart format across the touched files (GraphView.dart, Graph.dart, SugiyamaAlgorithm.dart, SugiyamaEdgeRenderer.dart, and example files), which accounts for most of the diff noise.
• Documented the new properties with a usage example in README.md.

Test plan

• flutter test passes
• Manually verified pan/zoom still works with default settings in the example app
• Manually verified scaleEnabled: false / panEnabled: false disable the respective gestures

[hiSandog]

Exposing the InteractiveViewer knobs makes sense, but this PR also includes formatting noise and unrelated equality/API cleanups, which will make review harder. It may be worth splitting the mechanical dart format / Edge.operator== changes from the new builder parameters. For the feature itself, a small widget test that passes non-default minScale, maxScale, panEnabled, and scaleEnabled through GraphView.builder would prove the wrapper preserves the previous defaults while honoring overrides.