feat: add support for Black Forest Labs Flux 2 Dev AI model

[Aulos]

Add type definitions for @cf/black-forest-labs/flux-2-dev model.

I am not sure why but this model is still not added to the available model list. The partnership was announced a month ago and it is in the docs.

It would be nice to have a better defined input, but the docs are quite lacking, so I assumed it handles same type as Request['body'], so ReadableStream<Uint8Array>.

Changes

• Input interface with multipart request support
• Output interface for Base64 image generation
• Base class implementation
• Model registration in AiModels interface

[github-actions[bot]]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}