- Add examples/kv_cache_multiturn_benchmark.py: realistic 15-turn tech
support conversation (~1500 history tokens) with scaling test at 4, 8,
12, and 16 messages to show speedup increasing with history length
- Add tests/test_past_kv_models.py: GPU integration tests for Llama,
Qwen3, and Gemma2 past_key_values generation plus tuple-KV v5 compat
- Add tests/test_past_kv_utils.py: CPU-only unit tests for
_ensure_cache_is_dynamic and _slice_position_ids utilities