refactor: simplify diffusion model runner params

[leejet]

Summary

• Replace wrapper-only diffusion model classes with DiffusionModelRunner, which inherits GGMLRunner, owns the tensor prefix, and lets concrete runners expose compute(DiffusionParams).
• Shrink DiffusionParams to common inputs plus typed model-specific extras.
• Remove ADM channel plumbing from diffusion/conditioner params and use the SDXL ADM width directly where needed.
• Fix Flex.2 latent concat handling so Flux control-only logic no longer overwrites Flex.2 inpaint/control concat tensors.

Related Issue / Discussion

N/A

Additional Information

N/A

Checklist

• I have read and confirmed this PR follows the contribution guidelines.