Fixes

• Ignore undefined objects in link annotation logic (fixes #191).
• Flatten indirect references in imported annotation dictionaries (fixes #195).

Tweaks

• Ensure newline before endobj token (fixes #184).
• Optimized fallback logic in flate decode method.
• Added tests for PHP 8.3.

Features

• Added PdfType::flatten() method, which flattens indirect objects to direct objects.