New Animation like Moving Letters Effect 15

@saurabhraj042 requested to add a new animated text like [Effect 15](https://tobiasahlin.com/moving-letters/#15)

Look at existing animation effects in the lib/src/ directory to understand the pattern. The new effect should mimic the linked 'Moving Letters Effect 15'. Check how animations are structured and test by adding the new effect to the example app. Ensure it follows the package's animation conventions and naming.

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