Improve migration mechanisms

We have migrations for both `SqliteStore` and `WebStore`. However, these are currently purely for schema changes. Similar to https://github.com/0xMiden/node/issues/1704, it would be nice to be able to enhance the functionality to involve Rust logic as well, enabling usecases like changing underlying data (fetch from the store, run some conversion/adjusting logic, and then upsert to the store). One thing to think through is if it makes sense to put at the `Store` level or if this something that we more generally will want from `Client` somehow.

Look at the existing migration mechanisms for SqliteStore and WebStore. Examine the linked issue #1704 from the node repository to understand the desired pattern of adding Rust logic for data transformation. Determine whether the new functionality belongs at the Store abstraction level or the Client level. Start by reviewing the store interfaces and migration code in the codebase.

Escrito por el modelo de indexación a partir del texto del issue.