Add range demo example

[zhassan-aws]

Description of changes:

Add an example that can be used to demo Kani.

Resolved issues:

Related RFC:

Optional #ISSUE-NUMBER.

Call-outs:

Testing:

• How is this change tested?

• Is this a refactor change?

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[jaisnan]

We should probably add the rectangle example as well somewhere for demonstrations, it has come in handy for demoing the extension.

[zhassan-aws]

It's available under https://github.com/model-checking/kani/tree/main/tests/cargo-kani/rectangle-example

[jaisnan]

It's available under https://github.com/model-checking/kani/tree/main/tests/cargo-kani/rectangle-example

I forgot completely. Thanks for reminding! And for this example.

[adpaco-aws]

Thanks @zhassan-aws !