test(ensemble): cover progress timer dispose and ListView scroll APIs

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Risky behavior now covered

• Progress indicator countdown timers (07e1786b): Ensures countdownTimer and mainTimer are cancelled when the widget is removed from the tree, preventing post-dispose setState and leaked periodic timers.
• ListView scroll position API (4f5052b1 / scroll helpers): Verifies scrollToOffset is a safe no-op without scroll clients, jumps to a pixel offset when not animated, and scrollToTop resets offset to zero.

Test files added/updated

• modules/ensemble/test/widget/progress_indicator_test.dart (new)
• modules/ensemble/test/widget/list_view_test.dart (extended)

Why these tests materially reduce regression risk

Progress countdown uses two concurrent timers; the prior bug left mainTimer running after dispose and called setState on an unmounted widget. A widget test that unmounts the indicator and advances time past the countdown catches timer leaks immediately.

scrollToOffset / scrollToTop are invoked from YAML/script and must not throw when the list is not laid out yet, and must move the attached ScrollController when clients exist. These tests lock in the controller guard and scroll behavior without brittle layout snapshots.

Validation

flutter test test/widget/progress_indicator_test.dart
flutter test test/widget/list_view_test.dart --name "scrollToOffset|scrollToTop|no-op"

All new tests pass. (An existing footer-scope ListView test in the same file can fail independently of this change.)