fix(table): handle HTML table captions correctly

[omda777]

Closes #635

This PR fixes incorrect handling of HTML elements in tables during HTML → CommonMark deserialization.
It ensures captions are properly parsed, normalized, and emitted as Markdown content preceding the table, while also fixing edge cases related to table headers and whitespace normalization.

Screenshots or Video

Input (HTML with element):

<table>
  <caption>Employee Details</caption>
  <thead>
    <tr>
      <th>Name</th>
      <th>Role</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Alice</td>
      <td>Engineer</td>
    </tr>
    <tr>
      <td>Bob</td>
      <td>Designer</td>
    </tr>
  </tbody>
</table>

the output:

**Employee Details**

| Name | Role |
|---------|---------|
| Alice | Engineer |
| Bob | Designer |

Related Issues

• Issue HTML Transform: Erronous HTML Table Parsing #635

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname

[omda777]

hi @mttrbrts Hope you're doing well
can review PR