[Parsing] Images nested in Form XObjects are not detected

Description

Raster images nested inside PDF Form XObjects are not detected by LiteParse.

Images attached directly to a page are discovered correctly, but images contained in a Form XObject are omitted, even when there is only one level of nesting.

This can cause:

• Incorrect per-page image counts and image coverage.
• Missing image references in Markdown output.
• Missing images when image extraction is enabled.
• Incorrect image-related complexity or OCR decisions.

Expected behavior

LiteParse should recursively discover image objects contained in Form XObjects and return their bounds in page coordinates.

Actual behavior

Only top-level page image objects are discovered. Image objects inside Form XObjects are not returned.