Add ZImageTransformer2DModel and ZImagePipeline to the diffusers library.

Add ZImageTransformer2DModel and ZImagePipeline to the diffusers library.: a task in HF ML Tasksmith (Harbor dataset). Custom attention processor ( ZSingleStreamAttnProcessor ): self-attention only (no cross-attention); applies QK norm (RMSNorm), RoPE via freqs cis , and SDPA. Raises ImportError…