Implements the missing document.createComment() DOM API method in the JSAR runtime. Previously, the method was declared in the JavaScript bindings but returned undefined instead of creating Comment nodes.

Changes Made

Core Implementation

• Document class: Added createComment(const std::string &data) method that creates Comment nodes with the specified text content and proper owner document reference
• JavaScript binding: Updated CreateComment method to properly validate arguments, create Comment nodes, and return them to JavaScript with appropriate error handling
• Include dependencies: Added necessary Comment class includes to both header and implementation files

DOM Integration

• Serialization support: Implemented Comment node serialization in HTMLDocument::SerializeFragment() to output proper HTML comment format (<!--content-->)
• Tree operations: Comment nodes now fully integrate with DOM tree operations like appendChild(), insertBefore(), etc.

Testing

• Added comprehensive test suite covering comment creation, node properties, DOM tree integration, and HTML serialization
• Tests verify compliance with Web API standards for node type, name, and content handling

API Usage

// Create a comment node
const comment = document.createComment('This is a comment');

// Add to DOM tree
document.body.appendChild(comment);

// Serializes correctly as HTML
console.log(document.body.innerHTML); // Contains <!--This is a comment-->

The implementation follows the MDN specification and DOM Standard, ensuring Comment nodes have correct properties (nodeType: COMMENT_NODE, nodeName: "#comment") and behavior.

Fixes #232.

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