fix: preserve Anthropic thinking blocks and signatures in LiteLLM round-trip#4999

giulio-leone wants to merge 5 commits intogoogle:maingoogle/adk-python:mainfrom

giulio-leone:fix/litellm-anthropic-thinking-roundtripgiulio-leone/adk-python:fix/litellm-anthropic-thinking-roundtripCopy head branch name to clipboard