[Wan 2.2 VAE] fix VAE tiling encode/decode

[miaojinc]

What does this PR do?

Current AutoencoderKLWan lacks some patchify stuff when tiling.
Also add patch_size config for Wan VAE unit tests.

Without this, we will got error likes:

  File "/home/mjc/diffusers/src/diffusers/pipelines/wan/pipeline_wan.py", line 645, in __call__
    video = self.vae.decode(latents, return_dict=False)[0]
  File "/home/mjc/diffusers/src/diffusers/utils/accelerate_utils.py", line 46, in wrapper
    return method(self, *args, **kwargs)
  File "/home/mjc/diffusers/src/diffusers/models/autoencoders/autoencoder_kl_wan.py", line 1248, in decode
    decoded = self._decode(z).sample
  File "/home/mjc/diffusers/src/diffusers/models/autoencoders/autoencoder_kl_wan.py", line 1204, in _decode
    return self.tiled_decode(z, return_dict=return_dict)
  File "/home/mjc/diffusers/src/diffusers/models/autoencoders/autoencoder_kl_wan.py", line 1374, in tiled_decode
    decoded = self.decoder(tile, feat_cache=self._feat_map, feat_idx=self._conv_idx)
  File "/root/miniforge3/envs/wan/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1773, in _wrapped_call_impl
    return self._call_impl(*args, **kwargs)
  File "/root/miniforge3/envs/wan/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1784, in _call_impl
    return forward_call(*args, **kwargs)
  File "/home/mjc/diffusers/src/diffusers/models/autoencoders/autoencoder_kl_wan.py", line 893, in forward
    x = up_block(x, feat_cache, feat_idx, first_chunk=first_chunk)
  File "/root/miniforge3/envs/wan/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1773, in _wrapped_call_impl
    return self._call_impl(*args, **kwargs)
  File "/root/miniforge3/envs/wan/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1784, in _call_impl
    return forward_call(*args, **kwargs)
  File "/home/mjc/diffusers/src/diffusers/models/autoencoders/autoencoder_kl_wan.py", line 709, in forward
    x = x + self.avg_shortcut(x_copy, first_chunk=first_chunk)
RuntimeError: The size of tensor a (2) must match the size of tensor b (4) at non-singleton dimension 2

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Who can review?

hi @yiyixuxu @a-r-r-o-w
Could you please help to review it, thanks