w3sper: Retrieve data-driver from node by contractId

[HDauven]

Summary

Enable clients to fetch a contract's data-driver from the node (if published by the owner), cache it locally, and auto-initialize it for immediate use.

Possible solution design or implementation

Add network.contracts.withId(id).driver.fetch() that returns the driver by downloading it and optionally verifying its integrity. It registers the driver through the DataDriverRegistry and returns it to the caller so it only needs to be used once.