refactor wan 2.2 image-to-video pipeline tests to the new mixin structure

[akshan-main]

What does this PR do?

Refactors the wan 2.2 image-to-video pipeline tests to the new mixin structure from #14113. The file covers two variants, so it keeps two config/test/memory triads: the 14B Wan22ImageToVideoPipeline (both transformers, boundary_ratio) and the 5B ti2v Wan225BImageToVideoPipeline (expand_timesteps). Both run on WanImageToVideoPipeline.

Existing coverage is kept for both: test_inference and test_save_load_optional_components (the 14B nulls transformer, image_encoder and image_processor via boundary_ratio=1.0; the 5B nulls transformer_2, image_encoder and image_processor). The 5B also keeps its test_components_function, the batch-single tolerance override, and the skipped test_callback_inputs. No caching tests are added since the old suite had none, and the attention-slicing test is dropped as the new framework has no equivalent.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Discussed on Slack with @sayakpaul
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

@sayakpaul

[Cyb3rLab5]

Nice work