fix(tv): handle key repeat events for D-pad navigation

[usmanvrtx]

Description

This PR fixes TV D-pad navigation when the user holds down a key (auto-repeat).
Previously only KeyDownEvent was handled, so repeated key events generated
while holding the D-pad button were ignored, causing slow/erratic scrolling and
navigation on TV remotes.

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)

What Has Changed

• Updated _handleScopeKeyEvent in TVFocusWidget to also handle KeyRepeatEvent, so held D-pad keys continuously trigger back/scope navigation instead of only the initial press
• Updated the onKeyEvent handler in TVScrollbarWidget to also handle KeyRepeatEvent, enabling smooth continuous scrolling while the UP/DOWN key is held

How to Test

1. Run the relevant TV tests (if any): flutter test modules/ensemble/test/widget/tv_scrollbar_widget_test.dart
2. On a TV/emulator, focus a ListView and hold the D-pad DOWN button — the list should scroll continuously while held
3. Hold the BACK button — it should keep triggering the back handler rather than only once
4. Verify normal single-press navigation still works as before

Screenshots / Videos

N/A

Checklist

• I have run flutter analyze and addressed any new warnings
• I have run flutter test and all tests pass
• I have tested my changes on the relevant platform(s)
• I have updated documentation if needed
• My changes do not introduce new warnings or errors