fix!: writeFile now requires filename

[Barbapapazes]

🔗 Linked issue

fix #66
close #76

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 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 PR solve a type issue and add some tests.

And because recast, https://github.com/benjamn/recast/blob/master/lib/parser.ts#L24, does not pass the filename to the parser option, we can't use it as the output filename.

I'm not sure if how tests are written is the best way to do it, so feel free to change it if you have a better idea.

📝 Checklist

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

[codecov]

Codecov Report

Merging #79 (59ac219) into main (a439ffa) will increase coverage by 1.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #79      +/-   ##
==========================================
+ Coverage   92.40%   93.48%   +1.07%     
==========================================
  Files          23       23              
  Lines        1751     1749       -2     
  Branches      322      327       +5     
==========================================
+ Hits         1618     1635      +17     
+ Misses        133      114      -19     

Files Changed	Coverage Δ
src/types.ts	100.00% <ø> (ø)
src/code.ts	97.77% <100.00%> (+20.85%)	⬆️