Validate mimeType in ImageContentBlock.FromBytes and AudioContentBlock.FromBytes#1321

stephentoub merged 3 commits intomainmodelcontextprotocol/csharp-sdk:mainfrom

copilot/fix-exception-for-null-mime-typemodelcontextprotocol/csharp-sdk:copilot/fix-exception-for-null-mime-typeCopy head branch name to clipboard