Fix: Android v1 compatibility issues, Dial responsiveness, negative duration, and null-safety issues

[MKMalik]

PR Description

This PR addresses several issues in the _Dial duration picker:

Immediate dial response

• Dial now responds immediately when dragging from any position, not just after 3 o’clock (15 mins).
• Removed outdated quadrant guards that caused delayed updates.

Prevent negative duration

• Dragging near 12 o’clock no longer produces negative values.
• _updateThetaForPan() now clamps the angle to zero if the resulting duration would be negative.

Null-safety compliance

• _position and _center are now safely handled as nullable.
• Guards added to prevent null-pointer exceptions on pan start/update.

Android v1 embedding compatibility

• Ensured gestures and animations behave correctly on older Android v1 embedding.
• Fixed any platform-specific issues with RenderBox offsets.

Flutter-specific adjustments

• _thetaTween and _thetaController animation updates now respect null-safety.
• Smooth transitions across 12 o’clock are preserved.
• Simplified angle calculation using consistent atan2 logic.

[MKMalik]

those in need can use this repo until it's merged
https://github.com/MKMalik/flutter_duration_picker.git