Add previews of button sizes

[koppen]

[Copilot]

Pull Request Overview

This PR adds previews for different button sizes in the demo and adjusts the small button padding. The change provides visual examples of all available button sizes (xs, sm, default, lg, xl) and standardizes the vertical padding for small buttons.

• Adds a new "Sizes" preview group showcasing all button size variants
• Updates the small button's vertical padding from py-1.5 to py-2

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
demo/test/components/previews/button_preview.rb	Adds preview methods for all button sizes with display configuration
app/components/flowbite/button.rb	Updates small button vertical padding for consistency

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