Remove json tags from internal structs

JSON marshaling uses field names directly; explicit tags
are unnecessary at this level.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/llm/message.go

@@ -29,13 +29,13 @@ type (
 	}
 
 	ToolCall struct {
-		ID       string       `json:"id"`
-		Function FunctionCall `json:"function"`
+		ID       string
+		Function FunctionCall
 	}
 
 	FunctionCall struct {
-		Name      string `json:"name"`
-		Arguments string `json:"arguments"`
+		Name      string
+		Arguments string
 	}
 
 	Tool struct {