Backlog#1845 step 7. The replication crate's hand-rolled, crate-generic Error type actually describes one thing: failures of the persisted resync/MRF state files. Rename it to ResyncStateError so the name says so, and stop collapsing io::Error into Other(String): a new Io(std::io::Error) variant keeps the kind and source chain, Display renders identically, and the ecstore boundary maps it to StorageError::Io so the kind survives into store-layer classification instead of degrading into a stringified other().
No thiserror introduced - the crate keeps its zero-internal-deps posture and hand-written impls.
Ref rustfs/backlog#1845
