- Remove DataContent.ContainsData. While ContainsData could be used to avoid lazily-instantiating a `ReadOnlyMemory<byte>` from a data URI, in all cases examined ContainsData was being used to guard accessing Data, in which case Data.HasValue is sufficient.- Make ToolMode optional. We'd previously said that an implementation could use null to imply None if it wanted, but with this being optional we'd want null to be the same as auto, so I added in an explicit null options. That matches as well with what various other client libs do.- Remove IChatClient/IEmbeddingGenerator.Metadata. GetService can be used instead, reducing what an implementer must implement and what's exposed to a consumer.- Add Complete{Streaming}Async for a single message. We have such accelerators in other places but not here, and it provides a natural grow-up from string to ChatMessage to `IList<ChatMessage>`.- Change UsageDetails.XxTokenCount properties from int? to long?. The AdditionalCounts is already based on longs, and in theory the token counts could exceed int, especially in a situation where UsageData is being used to sum many other call data.- Rename GenerateEmbeddingVectorAsync's TEmbedding to TEmbeddingElement. Everywhere else TEmbedding is used where it represents an Embedding, but here it represents a numerical element in an embedding vector.- Remove setters on FunctionCall/ResultContent for required ctor parameters. Having those setters goes against .NET design guidelines.- Remove FunctionResultContent.Name. It's unnecessary and is actually causing us to do more work in places.

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