migrate wan lora tests to the pipeline-level mixins

[akshan-main]

What does this PR do?

Migrates the Wan pipeline LoRA tests from tests/lora/test_lora_layers_wan.py to the pipeline-level mixins from #14268, following the Flux port: TestWanPipelineLoRA(WanPipelineTesterConfig, LoraTesterMixin) and TestWanPipelineLoRAMemory(WanPipelineTesterConfig, LoraMemoryTesterMixin) in tests/pipelines/wan/test_wan.py, and the old file removed.

The old file's specifics dissolve into the new structure: the text-encoder tests skip through _lora_loadable_modules (Wan loads LoRA into the transformers only), the two "Not supported in Wan" block-scale skips disappear since those tests now live in UNetLoraTesterMixin, and the old 9e-3 tolerance overrides are not needed at the mixin defaults (verified by running the classes). Follows #14268.

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

[sayakpaul]

/diffusers-bot pytest tests/pipelines/wan/test_wan.py -k "lora"

[github-actions]

✅ pytest tests/pipelines/wan/test_wan.py -k "lora" passed on GPU — view logs.