Add support for device API to `snaps-jest`

At a minimum we need:

- Support for all the RPC methods in the device API.
- The ability to create mocked devices, and read/write data with them.

Start at the snaps-jest entry point and review how the device API's RPC methods are exposed. Map the full device API surface and the mocked-device behavior needed for reading and writing data. Done means all device API RPC methods are supported and mocked devices can be created and used for data access.

Written by the indexing model from the issue text.