How the scroll view should respond to user input.
For example, determines how the scroll view continues to animate after the user stops dragging the scroll view (providing a custom implementation of ScrollPhysics.createBallisticSimulation allows this particular aspect of the physics to be overridden).
If an explicit ScrollBehavior is provided to scrollBehavior, the ScrollPhysics provided by that behavior will take precedence after physics.
Defaults to matching platform conventions.
The ScrollPhysics.applyBoundaryConditions implementation of the provided object should not allow scrolling outside the scroll extent range described by the ScrollMetrics.minScrollExtent and ScrollMetrics.maxScrollExtent properties passed to that method. If that invariant is not maintained, the nested scroll view may respond to user scrolling erratically.
final ScrollPhysics? physics;