Make the reading progress smoother

[luo-zhan]

PR Checklist

• The commit message follows guidelines for NexT.
• Tests for the changes was maked (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs in NexT website have been added / updated (for features).

PR Type

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Build related changes.
• CI related changes.
• Documentation content changes.
• Other... Please describe:

What is the current behavior?

The reading progress bar is a little stuck.

What is the new behavior?

Improve the accuracy of numerical value to make the progress bar smoother.

How to use?

In NexT _config.yml:

reading_progress:
  enable: true
  ...

Does this PR introduce a breaking change?

• Yes.
• No.

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[welcome]

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1 out of 2 committers have signed the CLA.

✅ stevenjoezhang
❌ luo-zhan
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