Add support for creating form fields

[ridgey-dev]

This update introduces a new add_form_field method that allows adding text fields to a PDF page with a custom appearance. The method supports:

• Specifying the page and rectangle coordinates for the field
• Generating an appearance stream with fill and border styling
• Adding the field to the page’s annotations and the document’s AcroForm fields
• This enhancement enables easier creation of interactive PDF forms programmatically.