Source code generation fails under 1.0.0-M1

Thank you for providing such a great tool! I also use it for my work. :)

When running under the following conditions, an error occurs, and the source code generation fails:

- Version: 1.0.0-M1
- Scala Version: 2.12.18 (intended for use with sbt-guardrail)
- JDK: Corretto-17.0.11.9.1

(I have masked the type names.)
```
FooBarType:
type: string
enum:
- A
- B
- C
- D
foo_type:
type: array
nullable: false
items:
allOf:
- $ref: '#/components/schemas/FooBarType'
```
```
sbt:my-project> guardrail
Error:Unknown type for the following structure (No type definition, class: io.swagger.v3.oas.models.media.ComposedSchema, .components.schemas.foo_type.items):
Tracker(class ComposedSchema {
class Schema {
}
}, Vector(.components, .schemas, .foo_type, .items))

[error] (Compile / guardrail) dev.guardrail.sbt.CodegenFailedException
[error] Total time: 1 s, completed 2024/09/05 16:20:55
```

Here is the code to reproduce the issue:
https://github.com/aoiroaoino/guardrail/commit/199dc9fd3b20cc88528942c5072c128135a67589

Could you please take a look? Thank you for your assistance.