Add input validation to evaluate_diffusion_model

[Copilot]

Description

evaluate_diffusion_model accepted all-optional parameters but would raise an opaque AttributeError at runtime when pipe=None and either autoround or model was also None. This adds a guard at the function entry point with a clear ValueError.

Changes:

• auto_round/eval/evaluation.py: Validate at the top of evaluate_diffusion_model that either pipe is provided, or both autoround and model are provided — before any imports or logic runs:

  if pipe is None and (autoround is None or model is None):
      raise ValueError(
          "Either 'pipe' must be provided, or both 'autoround' and 'model' must be provided."
      )

• test/test_cpu/advanced/test_evaluation_functions.py: Added TestEvaluateDiffusionModelValidation covering all three invalid-argument cases (all None, only autoround, only model).

Type of Change

• Bug fix
• New feature
• Documentation update
• Performance improvement
• Code refactoring
• Other (please specify):

Related Issues

Relates to #1522

Checklist Before Submitting

• My code has been tested locally.
• Documentation has been updated as needed.
• New or updated tests are included where applicable.

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