Consider deprecating `import_store`/`export_store`

On the webclient, it may make sense to deprecate raw store import/export as a public API. Today it is effectively an IndexedDB table dump: it exports every Dexie table, and `import` clears and replaces the target store, so the format is tightly coupled to internal schema details, client version behavior, and browser storage implementation.
I think it should not necessarily be the client's responsibility to manage the store as it is effectively the whole snapshot of state of the client. Rather, the user could be managing store instances and instantiating clients with the correct stores as needed (as it works on the Rust client), or exporting/importing the parts of the state they are interested in.

Look at the webclient's store import/export API, likely in files handling IndexedDB interactions or client initialization. Understand how `import_store` and `export_store` are currently used and their coupling to internal schema. Compare with the Rust client's approach to managing store instances. Determine what a deprecation path would involve, such as adding warnings, documenting alternatives, and possibly providing migration guidance.

Scritto dal modello di indicizzazione a partire dal testo della issue.