chore: add support for nested CSS

[onmax]

🔗 Linked issue

#371

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ 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

Adds support for nested CSS when the module parses CSS.

I don't want to create a lot of tests, so the test I have added is minimal but covers different nested CSS situations

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.50000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 84.54%. Comparing base (b726fa2) to head (4f4c8f6).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/plugins/transform.ts	87.50%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #384      +/-   ##
==========================================
+ Coverage   83.85%   84.54%   +0.68%     
==========================================
  Files          13       13              
  Lines        1016     1029      +13     
  Branches      266      270       +4     
==========================================
+ Hits          852      870      +18     
+ Misses        158      153       -5     
  Partials        6        6              

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