Encryption-secret exposure via disabled dependency zeroization

Memory exposure in Matrix.org vodozemac 0.5.0 through 0.5.1 allows local users to expose encryption secrets through process-memory access. The Cargo manifest disabled default features on the Dalek dependencies without enabling their zeroize feature, so the dependencies did not clear secret-bearing values on drop. Exploitation requires local low-privilege access to residual process memory; the result is limited to increased confidentiality risk from extra or longer-lived secret copies.