External CSS assets not being inlined when imported via ?inline #959

Reproduction link or steps

minimal reproduction: https://stackblitz.com/edit/github-2dddpu9g?file=src%2Findex.ts

• run npm run build
• examine output asset indist/index.js
• notice:
  • the contents of style.css are inlined (as expected, this is correct)
  • the contents of jodit/es2021/jodit.css are not inlined (not expected, this is the bug)
  • 

What is expected?

I would expect when ?inline is added to the import statement the contents of the file are inlined as a string and assigned to the import variable.

What is actually happening?

In tsdown, the import is being processed as a regular js import statement instead of an instruction to inline the css file as a string.

Any additional comments?

I have prepared the exact same case in Vite 8 library mode (same source files, same tsconfig) to show how it functions in comparison.

https://stackblitz.com/edit/vitejs-vite-2v5kn8ki?file=src%2Findex.ts

• run npm run build
• examine output asset indist/index.js
• notice:
  • the contents of style.css are inlined (as expected)
  • the contents of jodit/es2021/jodit.css are also inlined (as expected).
  •