Fix ListView owned ScrollController leak

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Bug and impact

Recent ListView scroll-control changes create a ScrollController in ListViewState whenever callers do not provide one. That controller was never disposed, so every mount/unmount of a ListView leaked a ChangeNotifier/ScrollController. Repeated navigation through list-heavy screens can accumulate leaked controllers and listeners, increasing memory usage and eventually causing user-facing instability.

Root cause

ListViewState moved ScrollController creation out of ListViewCore to support initialScrollOffset and scroll methods, but did not track whether the state owned that controller or dispose it during teardown.

Fix

Track the internally-created controller in ListViewState and dispose only that owned instance. Externally supplied controllers remain caller-owned.

Validation

• Added widget regression tests covering owned-controller disposal and external-controller ownership.
• Attempted to run flutter test modules/ensemble/test/widget/list_view_test.dart, but this runner does not have flutter installed on PATH.

  

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Note

Low Risk
Low risk: change is limited to widget lifecycle management and adds tests; main risk is unintended disposal behavior, mitigated by only disposing controllers created internally.

Overview
Fixes a ListView memory leak by tracking whether its ScrollController was created internally and disposing that owned controller in ListViewState.dispose().

Adds widget tests to verify internally-created controllers are disposed on unmount, while caller-provided controllers are left undisposed.

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