Fix dataset upload for >2GB files

[fm3]

Fixes seek offset integer overflow. All components fit comfortably into Int, but their product did not. We thought the product to be Long already, but there was a lossy conversion after all. Now we just make all the values in the upload service Long. Memory overhead should be negligible.

Steps to test:

• Upload a dataset as single zip that is >2GB in size
• Should upload correctly.

Issues:

• fixes Integer overflow when uploading dataset with large single file(s) #5888

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(Please delete unneded items, merge only when none are left open)

• Updated (unreleased) changelog
• Needs datastore update after deployment
• Ready for review