fix: Fixed broken include in the Ixa book. Fixes #302.

[RobertJacobsonCDC]

Fixed broken include in the Ixa book introduced by automated Rust formatting. Line lengths were also brought into line with our lints.

The #include is embedded in a Rust code fench:

```rust
// main.rs
{{ #include ../../models/basic/main.rs}}
```

"Autoformat on save" tries to format the include as Rust code and mangles it.

[cdc-as81]

LGTM