Repository::rev_parse_single("@{-1}") could return the previous object id from HEAD's reflog after the prior checkout branch had been deleted. Git treats @{-N} as the previous checkout name and reparses that name, so a deleted branch no longer names a single revision.

The regression adds deleted prior-checkout fixtures and asserts that @{-1} follows the Git baseline failure for deleted branch names while still accepting previous checkout names that are full object ids.

The fix keeps resolving existing prior checkout references as before, but only falls back to a direct object id when the reflog name itself is a full object id for the repository hash kind.

Git baseline: Git 2.50.1 rejects the deleted branch scenario with `git rev-parse --verify @{-1}` reporting "Needed a single revision" and exiting 128. The reference implementation in object-name.c expands @{-N} to the previous checkout text before normal revision lookup.

Validation:
- GIX_TEST_IGNORE_ARCHIVES=1 cargo test -p gix --test gix revision::spec::from_bytes::reflog::nth_prior_checkout_to_deleted_branch_fails_like_git --features revision
- GIX_TEST_IGNORE_ARCHIVES=1 cargo test -p gix --test gix revision::spec::from_bytes::reflog --features revision
- cargo test -p gix --test gix revision::spec::from_bytes::reflog --features revision
- GIX_TEST_IGNORE_ARCHIVES=1 cargo test -p gix --test gix revision::spec::from_bytes --features revision
- cargo test -p gix --test gix revision::spec::from_bytes --features revision