OAS 3.0 file upload generation fails

Trying to upgrade existing Guardrails project from 0.41.1 to 0.55.4 and Swagger 2 to OpenAPI 3, and having issues with file uploads. Guardrails is generating Akka Http endpoints.

When trying to attempt either recommended solution on the OAS website (https://swagger.io/docs/specification/describing-request-body/file-upload/) to posting a file upload, guardrails is generating errors.

Attempt 1:
```
openapi: 3.0.2
...
/uploadendpoint:
post:
...
requestBody:
required: true
content:
application/octet-stream:
schema:
type: string
format: binary
```
This fails to generate with `Error:Unable to generate decoder for application/octet-streams`

Attempt 2:
```
openapi: 3.0.2
...
/uploadendpoint:
post:
...
requestBody:
required: true
content:
multipart/form-data:
schema:
type: object
properties:
file:
type: string
format: binary
required:
- file
```
This fails to generate with `Unable to generate decoder for multipart/form-data`

It would be good not to have to post application/json and post a base64 encoded field (if that works, but not tested). The second attempt above is compatible with the old API and Swagger 2 (not the same way of declaring, but clients at runtime are compatible).

Perhaps I am doing something dumb, in which case I apologise in advance. Any help would be appreciated, and a confirmation what is possible would be great.