LanguageModelExtraDataPart- arbitrary model-specific data in request

[roblourens]

We can build prompt cache checkpoints on top of this, and anything else in the future.

/**
 * A language model response part containing arbitrary model-specific data, returned from a {@link LanguageModelChatResponse}.
 * TODO@API naming, looking at LanguageModelChatRequestOptions.modelOptions, but LanguageModelModelData is not very good.
 * LanguageModelOpaqueData from prompt-tsx?
 */
export class LanguageModelExtraDataPart {
	/**
	 * The type of data. The allowed values and data types here are model-specific.
	 */
	kind: string;

	/**
	 * Extra model-specific data.
	 */
	data: any;

	/**
	 * Construct an extra data part with the given content.
	 * @param value The image content of the part.
	 */
	constructor(kind: string, data: any);
}