feat: add new utility functions for CallToolResultContentItem

[hashemix]

📌 Summary

Added new utility functions for CallToolResultContentItem type, for easier conversion of call tool results into contents:

Example:

// get the content type
println!("{}",content.content_type())

// try to convert to TextContent
let text_content : TextContent = content.as_text_content().unwrap();

// try to convert to ImageContent
let image_content : ImageContent = content.as_image_content().unwrap();

// try to convert to EmbeddedResource
let embedded_resource : EmbeddedResource = content.as_embedded_resource().unwrap();

AudioContent (draft version of schema)

// try to convert to AudioContent
let audio_content : AudioContent = content.as_audio_content().unwrap();