feat: add support for bun

[danielroe]

🔗 Linked issue

resolves https://github.com/unjs/nypm/issues/86

❓ 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

This adds support for the bun package manager.

As Bun isn't yet corepack-supported (we can track in https://github.com/oven-sh/bun/discussions/4056) this directly runs the bun command.

📝 Checklist

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

[codecov[bot]]

Codecov Report

Merging #87 (f15eade) into main (69003dc) will increase coverage by 0.05%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
+ Coverage   98.02%   98.07%   +0.05%     
==========================================
  Files           5        5              
  Lines         405      416      +11     
  Branches       64       67       +3     
==========================================
+ Hits          397      408      +11     
  Misses          8        8              

Files Changed	Coverage Δ
src/_utils.ts	98.49% <100.00%> (+0.07%)	:arrow_up:
src/package-manager.ts	100.00% <100.00%> (ø)
src/types.ts	100.00% <100.00%> (ø)