Feature/gemini structured output support

[dev-billy]

Hey everyone! 👋
This is my first PR to Prism, so I’m pretty excited (and a little nervous 😅). I’ve added structured output support for the Gemini provider using a prompt-based approach, similar to how it’s done for Anthropic and Deepseek Providers.

What’s in this PR?

• Adds structured output for Gemini using prompt formatting.
• Includes tests to make sure everything works as expected.

Why this approach?

I noticed another PR #116 exploring structured output for Gemini with a schema-based approach. My take is a little different—more in line with how it is being handled for Anthropic. The only difference with anthropic, gemini api config allows for response_mime_type which when set to application/json ensures the response is a JSON

Would love your thoughts!

Since this is my first contribution, I’d really appreciate any feedback! Let me know if this makes sense or if there’s anything I can tweak.

Thanks for taking a look! Looking forward to your thoughts. 🚀😊

[pushpak1300]

Changes looks good.
I'll go over them once to make sure everything works perfectly.
Can you please update the docs as well ?

https://prism.echolabs.dev/providers/gemini.html
https://prism.echolabs.dev/getting-started/introduction.html

[dev-billy]

Thank you, yes let me update

[kinsta]

Preview deployments for prism ⚡️

Status	Branch preview	Commit preview
❌ Failed to deploy	N/A	N/A

Commit: e0860e281370031d21d805d15244679f2b076c27

Deployment ID: 6bdbdde0-ae6e-44f3-a3ee-6724fe542949

Static site name: prism-97nz9

[pushpak1300]

Overall Looks great.
Thank you for this. It will be great if you can do this changes.

[pushpak1300]

Again i guess this is correct but can you please keep the methods of this structured output as consistent across other provider so its easier to update or refactor any thing related to provider. for eg src/Providers/Anthropic/Handlers/Structured.php
Again this optional.

@sixlive what do you think.

[dev-billy]

I decided not to refactor the methods to be similar to the Anthropic Handler because the handle method feels bloated and might become difficult to follow through where exactly there's a failure if it does happen.

But also regarding consistency across other providers, the methods are similar to src/Providers/DeepSeek/Handlers/Structured.php and a bit similar to the OpenAI version but i guess the OpenAI case is different since it supports both JsonMode and StructuredMode for Structured Outputs