Log WanAnimate interpolation resizing as a warning

[wunianze666-netizen]

Summary

• replace the direct interpolation print(...) in WanAnimatePipeline.prepare_prev_segment_cond_latents() with logger.warning(...)
• add a regression test that captures the warning when previous-segment conditioning frames are resized

Why

This path runs inside library code, so writing directly to stdout makes the message harder to control in downstream applications. The rest of the pipeline already uses structured warnings for similar resizing notices.

Validation

• python -m pytest tests/pipelines/wan/test_wan_animate.py -k test_prepare_prev_segment_cond_latents_logs_interpolation_warning -q
• ruff check src/diffusers/pipelines/wan/pipeline_wan_animate.py tests/pipelines/wan/test_wan_animate.py
• ruff format --check src/diffusers/pipelines/wan/pipeline_wan_animate.py tests/pipelines/wan/test_wan_animate.py
• python -m py_compile src/diffusers/pipelines/wan/pipeline_wan_animate.py tests/pipelines/wan/test_wan_animate.py

Issue Linkage

This is a small logging cleanup and is not tied to an existing tracked issue.

[github-actions]

Hi @wunianze666-netizen, thanks for the PR! It does not appear to link an issue it fixes. If this PR addresses an existing issue, please add a closing keyword (e.g. Fixes #1234) to the PR description so the issue is linked. See the contribution guide for more details. If this PR intentionally does not fix a tracked issue, a maintainer can add the no-issue-needed label to silence this reminder.

[wunianze666-netizen]

Closing this one-off PR in favor of the pattern-level coordination in #14479. I will wait for maintainer confirmation there, consolidate the approved scope, run the current self-review workflow, and include exact test results before opening a replacement.