fix: object verson mtime

[JoshPigott]

Fixes #2311

Why

• All non-latest versions have the wrong mtime.
• This happens because the archived version is created by opening the current object and copying it, which changes the mtime instead of preserving the original.

Changes

• Keeping the original mtime.

Please let me know if you would like any changes. Thanks

[versity-github]

This won't automatically run in continuous integration without approval. A member of the Versity organization must allow it.