perf: avoid lowercasing long strings

[webstrand]

🔗 Linked issue

80

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [x] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

If the string is longer than nine characters it cannot possibly match any of the hard-coded strings. So wrap the lowercasing operation in a conditional that prevents the operation if the string is ten characters or longer.

📝 Checklist

• [x] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.

[pi0]

Perf gains are amazing! https://github.com/unjs/destr/commit/eb60af13cba90e26889892b4e9022749e3537b3f