refactor: convert hype train event to StyledText

[kevmo314]

Updates the text rendering in TwitchHypeTrainEventWidget to use StyledText() for a more flexible and maintainable approach to styling.

• Replaces Text.rich() with StyledText() for rendering text, aligning with the proposed resolution to utilize StyledText() for text styling.
• Utilizes tags within StyledText() to apply styles, specifically using the <b> tag to style certain text segments as bold, which is achieved through the StyledTextTag and leveraging the Theme.of(context).textTheme.titleSmall for styling.
• Maintains the original text content and structure, ensuring that the transition to StyledText() does not alter the message conveyed to the user.

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