fpdf2: Exponential SVG '<use>' expansion causes CPU and memory exhaustion in 'FPDF.image()'

fpdf2 is a PDF creation library for Python. From 2.5.0 until 2.8.8, fpdf2's SVGObject.build_xref() passes nested SVG <use> references to GraphicsContext.add_item(), whose default clone=True deep-copy behavior copies the complete referenced graphics tree during FPDF.image() processing. Repeating references at each nesting level makes the in-memory object count and processing work grow exponentially, allowing a small user-controlled SVG to consume excessive CPU and memory, raise MemoryError, fail PDF generation jobs, and reduce or exhaust worker capacity. ResourceAccessPolicy does not prevent the issue because the references are inline and require no external resource, XML entity, local file, or permissive network setting. This issue is fixed in version 2.8.8.