feat: concat support for mcp_tool macro

[hashemix]

📌 Summary

add concat!() support for mcp_tool macro

Example usage:

#[mcp_tool(
    name = "say_hello",
    description = concat!("Accepts a person's name" ,"and says ", "a personalized \"Hello\" to that person")
)]
#[derive(Debug, ::serde::Deserialize, ::serde::Serialize, JsonSchema)]
pub struct SayHelloTool {
    /// The name of the person to greet with a "Hello".
    name: String,
}