Public façade for WhatsApp app-state sync.

This module is the stable entry point; the work lives in five modules, each with one reason to change:

• ExWapp.AppState.Engine.Builders — build outgoing patch descriptions (contact, archive, pin, mute, delete, mark-read, clear-chat)
• ExWapp.AppState.Engine.Codec — encode/decode patches, mutation MACs, snapshot verification and the LTHash chain
• ExWapp.AppState.Engine.Sync — the IQ round-trips with the server, external blob download, and applying collection responses
• ExWapp.AppState.Engine.Dispatch — turn decoded mutations into contact and chat updates
• ExWapp.AppState.Engine.State — persist collection versions, hashes and mutation MACs

Reference: whatsmeow appstate/encode.go, appstate/decode.go, appstate.go.

The types for the shapes crossing this boundary (patch_info, mutation_info, hash_state, decoded_mutation) are declared where they are produced, in Builders and Codec.