Deep Dive into Temporal Workflow stress testing

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Introduces two stress testing scenarios ('rabbit' and 'reactor') for Temporal. The 'rabbit' scenario tests Workflow tree spawning, completion, termination, and cancellation with varying fan-out and depth. The 'reactor' scenario tests sustained load from signals on long-running Workflows. Details specific bugs found in cancellation/termination propagation and handling, including race conditions and nil pointer exceptions.