[video_player] Add durationUpdate to VideoEventType

[Andro999b]

Some custom video_platform implementation can update a duration during playback (like media_kit) for HLS streams (if they detected as a livestream). To address this new VideoEventType added: durationUpdate.

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[gemini-code-assist]

Code Review

This pull request introduces a new durationUpdate event to allow for changes in video duration during playback, which is useful for formats like HLS live streams. The VideoPlayerController is updated to handle this event and update its duration value accordingly. A new test is added to verify this functionality. My feedback focuses on improving the clarity and correctness of the new test case.

[gemini-code-assist]

The test name 'buffering status' is misleading as this test verifies the duration update functionality. It's also a duplicate of another test name in this file, which can cause confusion. It should be renamed to be more descriptive. Additionally, an extra blank line can be removed for conciseness.

Suggested change

	testWidgets('buffering status', (WidgetTester tester) async {
	final VideoPlayerController controller =
	VideoPlayerController.networkUrl(_localhostUri);
	await controller.initialize();
	const Duration initDuration = Duration(milliseconds: 100);
	controller.value = controller.value.copyWith(duration: initDuration);
	final StreamController<VideoEvent> fakeVideoEventStream =
	fakeVideoPlayerPlatform.streams[controller.playerId]!;
	const Duration updatedDuration = Duration(milliseconds: 200);
	fakeVideoEventStream.add(
	VideoEvent(eventType: VideoEventType.durationUpdate, duration: updatedDuration),
	);
	await tester.pumpAndSettle();
	expect(controller.value.duration, updatedDuration);
	await tester.runAsync(controller.dispose);
	});
	testWidgets('duration is updated by durationUpdate event', (WidgetTester tester) async {
	final VideoPlayerController controller =
	VideoPlayerController.networkUrl(_localhostUri);
	await controller.initialize();
	const Duration initDuration = Duration(milliseconds: 100);
	controller.value = controller.value.copyWith(duration: initDuration);
	final StreamController<VideoEvent> fakeVideoEventStream =
	fakeVideoPlayerPlatform.streams[controller.playerId]!;
	const Duration updatedDuration = Duration(milliseconds: 200);
	fakeVideoEventStream.add(
	VideoEvent(eventType: VideoEventType.durationUpdate, duration: updatedDuration),
	);
	await tester.pumpAndSettle();
	expect(controller.value.duration, updatedDuration);
	await tester.runAsync(controller.dispose);
	});