Merge `@linera/client` into `linera-protocol` to facilitate testing

[Twey]

It would be helpful to have some end-to-end tests in linera-protocol that include our JavaScript client library. Unfortunately, with @linera/client in a separate repository, this is difficult to achieve.

Let's merge @linera/client into the linera-protocol repository, along with the hosted examples, and leave this repository for the extension.

[deuszx]

This is now done, right @Twey ?