Deep Dive into Temporal Workflow stress testing

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.