fix: ScrollableControl.auto_scroll not working when scroll property is not explicitly set

[ndonkoHenri]

Fix #6397

The auto_scroll feature on scrollable controls (ListView, GridView, Column, Row, etc.) silently did nothing unless the scroll property was also explicitly set. This was because the auto-scroll logic in scrollable_control.dart was nested inside a scrollConfiguration != null check. Moved it outside so auto-scroll works independently.

Test Code

https://flet.dev/docs/controls/listview/#examples

Summary by Sourcery

Bug Fixes:

• Fix auto_scroll on scrollable controls so it works even when the scroll property is not explicitly set.

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Pull request overview

Fixes ScrollableControl.auto_scroll so it works even when the scroll property isn’t explicitly set (i.e., when no scrollbar configuration is provided).

Changes:

• Removes the dependency on scrollConfiguration != null for triggering auto_scroll.
• Always schedules a post-frame scroll-to-end animation when auto_scroll is enabled.

Comments suppressed due to low confidence (1)

packages/flet/lib/src/controls/scrollable_control.dart:107

• auto_scroll now schedules an animateTo() even when scrollConfiguration is null. In cases where this widget created its own _controller and the child is not wrapped into a Scrollable (e.g., wrapIntoScrollableView is true but scrollConfiguration == null returns widget.child), _controller may have no clients and _controller.position / animateTo() will throw at runtime. Consider guarding inside the post-frame callback with if (!mounted || !_controller.hasClients) return; before reading _controller.position, and optionally avoid animating when already at the target offset.

    if (widget.control.getBool("auto_scroll", false)!) {
      WidgetsBinding.instance.addPostFrameCallback((_) {
        _controller.animateTo(
          _controller.position.maxScrollExtent,
          duration: const Duration(seconds: 1),
          curve: Curves.ease,
        );
      });

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[FeodorFitsner]

Change the base of this PR to release/v0.85.0 and add changelog record.