[Interactive Book] fix parsing `sup` HTML tag

[aman-singh7]

Describe the bug The HTML tag sup is not properly parsed on a screen in Interactive Book.

Screenshots

• OS: Android

Are you working on this issue? (Yes/No) Yes

[aman-singh7]

@manjotsidhu please assign this to me.

[manjotsidhu]

This issue might give you a little bit of hard time as flutter_markdown was buggy. We are using our own fork of it, check https://github.com/CircuitVerse/packages. Feel free to open PR to that repo as we haven't kept that fork up to date with the new changes from https://github.com/flutter/packages