fix: implement CharacterData DOM API for jQuery DataTables compatibility (#73)

jQuery DataTables references the standard CharacterData interface which
was undefined in obscura's DOM environment, causing ReferenceError and
empty page renders.

- Add CharacterData class extending Node with data/length/substringData/
  appendData/insertData/deleteData/replaceData
- Make Text and Comment extend CharacterData instead of Node
- Update _wrap() to create proper Text/Comment instances by nodeType
- Add create_comment_node op for Document.createComment()
- Fix set_text_content to handle Comment node mutations

Fixes #72

Co-authored-by: KuaaMU <[email protected]>

crates/obscura-js/src/ops.rs

@@ -228,8 +228,10 @@ fn op_dom(state: &OpState, #[string] cmd: String, #[string] arg1: String, #[stri
         "set_text_content" => {
             let nid = arg1.parse::<u32>().unwrap_or(0);
             dom.with_node_mut(NodeId::new(nid), |n| {
-                if let NodeData::Text { contents } = &mut n.data {
-                    *contents = arg2.clone();
+                match &mut n.data {
+                    NodeData::Text { contents } => { *contents = arg2.clone(); }
+                    NodeData::Comment { contents } => { *contents = arg2.clone(); }
+                    _ => {}
                 }
             });
             "true".into()
@@ -246,6 +248,9 @@ fn op_dom(state: &OpState, #[string] cmd: String, #[string] arg1: String, #[stri
         "create_text_node" => {
             dom.new_node(NodeData::Text { contents: arg1.clone() }).index().to_string()
         }
+        "create_comment_node" => {
+            dom.new_node(NodeData::Comment { contents: arg1.clone() }).index().to_string()
+        }
         "element_children" => {
             let nid = arg1.parse::<u32>().unwrap_or(0);
             let ids: Vec<i32> = dom.children(NodeId::new(nid)).iter()