fix(isValidNodeImport): detect invalid cjs modules

[pi0]

🔗 Linked issue

Resolves #186

❓ 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

We check for valid ESM modules to either use .mjs entries or type: "module" (this could later be improved to double check syntax on ESM too)

But when detecting valid CJS entries, we have to make sure there is no mixed syntax before validating module.

📝 Checklist

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

[codecov]

Codecov Report

Merging #187 (9dc8116) into main (b7adabf) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #187   +/-   ##
=======================================
  Coverage   86.99%   86.99%           
=======================================
  Files           8        8           
  Lines        1007     1007           
  Branches      167      166    -1     
=======================================
  Hits          876      876           
  Misses        131      131           

Files Changed	Coverage Δ
src/syntax.ts	96.93% <100.00%> (ø)

[danielroe]

👌