perf: Clean up resources with docling-parse v4, no parsed_page output by default (#2105)

* Call PdfDocument.unload_pages from the pipelines where needed, delete parsed_page data unless requested to keep

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* pin docling-parse and update lock

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* Reinstate pipeline_options.generate_parsed_page

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

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Signed-off-by: Christoph Auer <cau@zurich.ibm.com>
Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>
Co-authored-by: Michele Dolfi <dol@zurich.ibm.com>