feat: add contructor utility functions to entity and attribute

01.workspace/heave/src/str/attribute.rs

@@ -5,3 +5,12 @@ pub struct O {
     pub id: String,
     pub value: Value,
 }
+
+impl O {
+    pub fn new(id: &str, value: Value) -> Self {
+        Self {
+            id: String::from(id),
+            value,
+        }
+    }
+}

01.workspace/heave/src/str/entity.rs

@@ -5,3 +5,17 @@ pub struct O {
     pub class: String,
     pub attributes: std::collections::HashMap<String, Attribute>,
 }
+
+impl O {
+    pub fn new(class: &str) -> Self {
+        Self {
+            class: String::from(class),
+            attributes: std::collections::HashMap::new(),
+        }
+    }
+    pub fn with_attribute(mut self, id: &str, value: Value) -> Self {
+        let attribute = Attribute::new(id, value);
+        self.attributes.insert(attribute.id.clone(), attribute);
+        self
+    }
+}