Fix HTML attribute compatibility with Tiptap JS

[sonnymilton]

Summary

Improve HTML parsing and rendering compatibility with Tiptap JS:

• Parse task item state from the data-checked attribute.
• Support both the current colwidth table attribute and legacy data-colwidth.
• Render both table width attributes to preserve backward compatibility.
• Prefer colwidth when both table width attributes are present.

Tests

Added regression coverage for:

• Checked, unchecked, and empty data-checked values.
• Parsing the JavaScript colwidth attribute.
• Compatibility with legacy data-colwidth.
• Table width rendering.

Compatibility

Verified against Tiptap JS 3.27.3.