docs: clarify isNpmBuiltinName function comment

Specify that the function checks for Node.js built-in module names
rather than just 'built-in module name' for better clarity.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jdalton

src/purl-type.ts

@@ -166,7 +166,7 @@ const getNpmLegacyNames = (() => {
 })()
 
 /**
- * Check if npm identifier is a built-in module name.
+ * Check if npm identifier is a Node.js built-in module name.
  */
 const isNpmBuiltinName = (id: string): boolean =>
   getNpmBuiltinNames().includes(id.toLowerCase())