feat: mark Function trait as Send (#12)

Allow to use Client in places that are also Send.

src/v1/tool.rs

@@ -133,7 +133,7 @@ pub enum ToolChoice {
 // Custom
 
 #[async_trait]
-pub trait Function {
+pub trait Function: Send {
     async fn execute(&self, arguments: String) -> Box<dyn Any + Send>;
 }
 

tests/v1_tool_test.rs

@@ -0,0 +1,7 @@
+use mistralai_client::v1::client::Client;
+
+trait _Trait: Send {}
+struct _Foo {
+    _dummy: Client,
+}
+impl _Trait for _Foo {}