4.0.0

feat: restructure progress bar API with new segment configuration

Redesign the progress bar model to better support flexible layouts and segment positioning. Replace label-based configuration with a more intuitive left/right pair structure and introduce dedicated segment configuration.

Key changes:
- Replace ProgressBarLabel with ProgressBarLabelPair for clearer left/right positioning
- Remove ProgressBarLabelPosition enum in favor of explicit left/right fields
- Add ProgressBarSegment and ProgressBarSegments for better segment control
- Replace segment_icon field with structured segments configuration
- Add new ProgressBarSegmentPosition enum supporting LEFT, RIGHT, and FULL_WIDTH

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