Remove dependency on external library for Ownership example

[bitzoic]

Description

It was noted that in the case of a breaking change to the std-lib, the external Ownership library would need to be updated, which depended on the std-lib creating a circular dependency.

The external library has been removed from the example and a skeleton of its implementation has been added with a link to the actual implementation.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.