fix: adapt to Ollama client 0.4.0

[anakin87]

Related Issues

• tests are failing: https://github.com/deepset-ai/haystack-core-integrations/actions/runs/11963832597/job/33355031427
• yesterday, a new version of the Ollama python client was released: they introduce pydantic and this breaks some of our assumptions to use python dictionaries
• See https://github.com/ollama/ollama-python/releases/tag/v0.4.0; add pydantic for validation and serialization ollama/ollama-python#276

Proposed Changes:

• update our code to make it work with ollama>=0.4.0
• pin ollama>=0.4.0

How did you test it?

CI, manual tests

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[Amnah199]

LG!