GHSA-68P4-PJPF-XWCQ insert_slice_clone can double drop if Clone panics.

Affected versions of this crate used ptr::copy when inserting into the middle of a Vec. When ownership was temporarily duplicated during this copy, it calls the clone method of a user provided element. This issue can result in an element being double-freed if the clone call panics. Commit 20cb73d...