Rust + Sway integration testing

A cargo-generate template that makes it easy to initialise Rust integration testing within an existing Sway project.

This template is designed for Rust developers who wish to test integration of their Rust application and Sway code.

The template on master follows the default-branch Sway SDK harness. For released projects, use the template from the Sway tag matching your Forc version.

See the Testing with Rust chapter of the default-branch Sway Book for a thorough guide on how to use this template.