Add JSON mode support for Gemini models

[KotlinFactory]

Gemini models support a native JSON mode via the responseMimeType parameter, but this is not currently exposed through AnyLanguageModel.

Proposed Solution

Extend the existing GenerationOptions for GeminiLanguageModel.

1. Set responseMimeType: "application/json" for Gemini requests
2. Optionally supports responseSchema for typed JSON output

Use Case

Structured outputs for:

• Data extraction
• Tool/function calling
• API response formatting

[KotlinFactory]

Should I create a PR for that? @mattt

[mattt]

@KotlinFactory This is a great feature request. I went ahead and opened a PR implementing that here: #80

[mattt]

This seems to be working well. Let me know if you have any suggestions for making this even better. Otherwise, look out for a new minor release with this in the next day or two. Thanks again for your help with this project, @KotlinFactory ✌️