Structured outputs for Anthropic / Gemini / Ollama

[marklysze]

Why are these changes needed?

Adding support for use of structured outputs for the Anthropic, Gemini, and Ollama client classes.

Related issue number

Closes #321

Checks

• I've included any doc changes needed for https://docs.ag2.ai/. See https://docs.ag2.ai/docs/contributor-guide/documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[marklysze]

Thanks @sternakt!