fix(anvil): backwards compatible dumps

[bernard-wagner]

Motivation

Fixes #8501

Solution

#8411 broke backwards compatibility of anvil state dumps. This PR allows anvil to handle both new and old dump formats.

Some additional test

Passes

git checkout 31628d1457f28405c8aa98751ac933f10a95b1c1 && git checkout HEAD^ # commit before PR #8411 
git cherry-pick 8e5001dcef4139a21f6a4ef31c902774d51eec66 # cherry-pick tests
cargo test --package anvil --test it -- state::can_load_existing_state_legacy

Fails

git checkout master
git cherry-pick 8e5001dcef4139a21f6a4ef31c902774d51eec66  # cherry-pick tests
cargo test --package anvil --test it -- state::can_load_existing_state_legacy

[mattsse]

ty

[noahlitvin]

@bernard-wagner thank you!!