Option to specify `outExtension` for generated dts files?

Like we can modify output extension of JavaScript files is there also a way to do the same for type definition files?

I tried returning this because `dts` was showing up in the autocomplete return options but it doesn't work.

```ts
format: ['cjs', 'esm'],
outExtension({ format }) {
switch (format) {
case 'cjs': {
return { js: '.cjs', dts: '.d.cts' };
}
case 'esm': {
return { js: '.mjs', dts: '.d.mts' };
}
default: {
return { js: '.js', dts: '.d.ts' };
}
}
}
```

Output type definition files generated after building have extensions `.d.ts` and `.d.cts` which is the default since my package is of type module. Is there a way to do this?

No files or tests are named. Start by tracing how tsup handles the existing outExtension callback for JavaScript and how declaration files are generated; determine where the dts output extension is selected. Done means the requested .d.cts and .d.mts extensions can be selected consistently for the cjs and esm formats, with coverage for the behavior.

Written by the indexing model from the issue text.