Display ZIP compression method in gallery file info, and optionally allow converting a gallery ZIP to store mode

Describe the feature you'd like

When a gallery is backed by a ZIP archive, the archive's compression method should be exposed in the gallery file info, so users can see whether it is Stored, Deflated, or Mixed. Optionally, a way could be provided to convert an existing ZIP gallery from Mixed/Deflated to fully Stored.

I'm not sure whether rewriting a user's source archive fits the project's design goals, so the conversion is optional or can be implemented in a plugin.

Describe the benefits this would bring to existing users

The documentation in Help > Images and Galleries states that

For best results, images in zip file should be stored without compression (copy, store or no compression options depending on the software you use. Eg on linux: zip -0 -r gallery.zip foldertozip/). This impacts heavily on the zip read performance.

In my own library I regularly hit 5–10 second stalls when opening some galleries. With this new feature, users can see whether a given gallery actually meets this recommendation and decide whether to convert it.

Is there an existing way to achieve this goal?

For identifying compression, a user can run zipinfo -v gallery.zip. For conversion, a user can extract the archive and rebuild it with zip -0 -r gallery.zip foldertozip/ as recommended in the documentation. These are outside Stash and require per-file manual work.

Have you searched for an existing open/closed issue?

• I have searched for existing issues and none cover the core request of my proposal

Additional context

No response