fix: fail fast when LiteLLM file_uri MIME type cannot be determined#5182

YizukiAme wants to merge 2 commits intogoogle:maingoogle/adk-python:mainfrom

YizukiAme:clean/litellm-file-uri-mimeYizukiAme/adk-python:clean/litellm-file-uri-mimeCopy head branch name to clipboard