Support ]]> escaping in dat method #230

Is your feature request related to a problem? Please describe.
Currently, calling .dat() with a string containing ]]> throws a "The string contains invalid characters." error. This requires developers to implement a custom function that split the CDATA section manually (e.g., before]]>after → <![CDATA[before]]><![CDATA[]]]]><![CDATA[>]]><![CDATA[after]]>).

While it's unlikely that a string like ]]> would appear in typical content, defensive escaping is necessary when converting user-generated content into RSS feeds.

Describe the solution you'd like
The .dat() method should automatically split ]]> sequences into separate CDATA sections, rather than throwing an error. Alternatively, a dedicated method like .escapedDat() that handles ]]> escaping would also work.

Describe alternatives you've considered
As a workaround, I'm currently splitting the string at every ]]> occurrence and calling .dat() multiple times to produce separate CDATA sections:

const addEscapedDat = (node, text) => {
  for (const [i, part] of text.split(']]>').entries()) {
    if (i > 0) {
      node.dat(']]')
      node.dat('>')
    }
    node.dat(part)
  }
  return node
}

Additional context
Add any other context about the feature request here.