Add cyclic workload and fixed-workers control arm tests

Replace 9 per-gen EMA controller tests with 7 random walk tests:
- test_config_has_adaptive_workers: API key exists, >= 2
- test_stats_has_prev_cost: prev_cost_per_obj_ns exists
- test_stats_has_last_generation: last_generation in {0,1,2}
- test_workers_within_bounds_after_collections: 100 collections, bounds check
- test_no_crash_varying_heaps: 100 collections with random heap sizes
- test_cyclic_workload_no_degradation: 3 phases cycling with bounds checks
- test_random_walk_vs_fixed_workers: control arm comparing walk vs fixed-4

Author: SonicField