[WAN] Adds VACE conditioning to WAN 2.1 (#304)

* Adds a VACE transformer block

* Adds the VACE logic to WAN

* Adds a pipeline to run WAN-VACE models

* Adds the logic to condition on videos and masks

Co-authored-by: ninatu <ninashv@google.com>

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Co-authored-by: ninatu <ninashv@google.com>

Author: martinarroyo