Prevent chat window corner radius getting stuck after back gesture is cancelled

[ateeb-infocusp]

First time contributor checklist

• I have read [how to contribute](https://github.com/signalapp/Signal-Android/blob/main/CONTRIBUTING.md) to this project
• I have signed the [Contributor License Agreement](https://signal.org/cla/)

Contributor checklist

• I am following the [Code Style Guidelines](https://github.com/signalapp/Signal-Android/wiki/Code-Style-Guidelines)
• I have tested my contribution on these devices:

• Samsung S23 Ultra, Android 16.0
• Google Pixel 7, Android 15.0
• Google Pixel 5, Android 13.0

• My contribution is fully baked and ready to be merged as is
• I ensure that all the open issues my contribution fixes are mentioned in the commit message of my first commit using the Fixes #14526 (Chat window remains rounded after cancelling system back gesture #14526)

---

Description

Enhanced the navigation state machine to explicitly handle cancelled gestures and refined the animation logic to ensure smooth transitions when a user starts, completes, or abandons a predictive back action. This prevents UI elements from getting "stuck" in intermediate states and ensures a good feel during navigation.

Main Changes

• Introduced NavigationState.CANCEL: Added a dedicated state to the AppScaffoldNavigator to handle cases where a user starts a back gesture but moves their finger back to the edge to cancel it.

• Refined State Transitions:

  • AppScaffoldNavigator now detects a 0f seek fraction to trigger the CANCEL state.
  • Added wasSeekInProgress tracking to ensure navigateBack always triggers the appropriate RELEASE animation if a gesture was recently active.

• Animation Logic Updates:

  • Updated AppScaffoldAnimationStateFactory to provide specific animation states for CANCEL, ensuring panes slide back into their original positions correctly.
  • Optimized defaultDetailReleaseAnimationState by removing redundant remember blocks and ensuring properties like corners reset to 0.dp upon completion.

• Code Cleanup: Simplified animator implementations in AppScaffoldAnimators.kt for better maintainability and more predictable animation behavior.