fix: apply idefics3 \n\n tokenization fix to colmodernvbert processing
ColModernVBert's processing_colmodernvbert.py is generated from modular_colmodernvbert.py
which inherits from idefics3. Sync the _get_num_multimodal_tokens fix (extra_split_newline)
so check_modular_conversion.py passes.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>