cant see blinking cursor in TypewriterAnimatedText

**Describe the bug**
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**To Reproduce**
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1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Expected behavior**
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**Screenshots**
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**Flutter:**
- version
- channel

**Dart:**
- version

**Additional context**
Add any other context about the problem here.

Look at the TypewriterAnimatedText widget in the codebase to understand how the blinking cursor is implemented. Check the widget's properties and animation logic. Reproduce the issue in a Flutter app using the package to see the missing cursor. Verify the fix by running the example app or writing a test.

索引モデルが issue の本文から書いたものです。