Custom Class Serialization in Workflow DevKit

Vercel's Workflow DevKit now supports custom class serialization via the new @workflow/serde package. Developers can define how their class instances are serialized and deserialized across workflow and step function boundaries by implementing two static methods using WORKFLOW_SERIALIZE and WORKFLOW_DESERIALIZE symbols. The feature is demonstrated using the @vercel/sandbox class, where instances are automatically converted to plain data when crossing step boundaries and reconstructed on the other side, enabling seamless passing of complex objects in durable workflows.