Multi-controlnet batching for `StableDiffusionXLControlNetInpaintPipeline`

**Is your feature request related to a problem? Please describe.**
Currently, batching is not supported when we are conditioning the SDXL pipeline on multiple controlnets: https://github.com/huggingface/diffusers/blob/28f9d84549c0b1d24ef00d69a4c723f3a11cffb6/src/diffusers/pipelines/controlnet/pipeline_controlnet_inpaint_sd_xl.py#L771

**Describe the solution you'd like.**
We can pass a list of lists of images for batch inference.

**Describe alternatives you've considered.**
One-by-one processing, which results in very low GPU utilization.

There was a similar PR raised for the `StableDiffusionControlNetPipeline` https://github.com/huggingface/diffusers/pull/6334

src/diffusers/pipelines/controlnet/pipeline_controlnet_inpaint_sd_xl.py の参照されているバッチ処理ロジックから始めます。要求されている list-of-lists 入力を、PR #6334 の StableDiffusionControlNetPipeline に対する同様の変更と比較します。完了条件は、multi-ControlNet SDXL inpaint 推論がバッチ入力を受け付け、1 件ずつの処理を避けることです。

索引モデルが issue の本文から書いたものです。