Introducing Modal Batch: Process 1 million jobs with 1 line of code

Introduces Modal Batch, a new interface backed by a durable queue system for massive job processing. Enhancements include a 500x increase in input capacity (1 million inputs), guaranteed execution for up to 7 days, and a native `.spawn_map` handler for batch input processing. This builds upon existing dynamic batching capabilities by providing a more robust and scalable solution for tasks like data preprocessing, embedding generation, and training data preparation.