feat: improve file cli tool support (#80)

with `toIum` `mimetype: application/zip`,
`file` cli tool now detect `Zip data (MIME type "application/zip"?)` instead `Zip data (MIME type "application/zipN"?)`

MacOS still unable to unarchive produced files.
It has weird behavior with zip files containing `mimetype` uncompressed as first file entry.

```
printf 'application/zip' > mimetype
printf 'Hello World!' > file.txt
zip -0 -X zip-mimetype-X.zip mimetype file.txt
```

And macos is unable to extract this archive...

Closes: #79
Refs: https://github.com/tpoisseau/repro-zip-js-macos-issue

Author: tpoisseau

src/ium/to_ium.ts

@@ -88,8 +88,11 @@ export async function toIum(
   );
   await zipWriter.add('mimetype', new TextReader(mimetype), {
     compressionMethod: 0,
-    dataDescriptor: false, // ensures the data length is written in the local file header
-    extendedTimestamp: false, // smaller payload, the extra field is empty
+    // ensures the data length is written in the local file header
+    dataDescriptor: false,
+    dataDescriptorSignature: false,
+    // smaller payload, the extra field is empty
+    extendedTimestamp: false,
   });
 
   const sources: ToIumIndex['sources'] = [];