feat(tab-bar): add customizable divider thickness

[usmanvrtx]

Description

This PR adds configurable divider thickness and padding to the Ensemble TabBar, including the TV TabBar implementation.

Related Issue

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

TabBar divider styling

• Added dividerThickness to configure the TabBar divider height, defaulting to 1.
• Added dividerPadding to configure divider insets and vertical spacing.
• Applied divider styling consistently to standard and TV TabBar implementations, including spacing before the TV focus indicator.
• Added schema metadata for the new TabBar properties.

How to Test

1. From modules/ensemble, run flutter analyze.
2. From modules/ensemble, run flutter test.
3. Verify TabBar styling with YAML similar to:

TabBar:
  styles:
    dividerColor: 0xFF666666
    dividerThickness: 3
    dividerPadding: [16, 4, 16, 8]

4. Confirm that existing TabBar layouts without the new properties retain the default divider behavior.

Screenshots / Videos

Not included.

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 where applicable
• My changes do not introduce new warnings or errors