Add WAN Animate pipeline with face motion pre-computation

- Add WanAnimateTransformer3DModel with motion encoder, face encoder,
  and face adapter cross-attention blocks
- Add WanAnimatePipeline supporting animate and replace modes with
  multi-segment temporal stitching
- Add generate_wan_animate.py inference entrypoint
- Add base_wan_animate.yml config for 720p inference
- Pre-compute face motion vectors once per segment instead of every
  denoising step for faster inference
- Simplify face block cross-attention forward pass: replace einops
  with jnp.reshape, remove redundant sharding constraints
- Add parity tests for animate modules and diffusers comparison