Production Gralkor.Client implementation. In-process — no HTTP — talks
to graphiti via Gralkor.GraphitiPool (Pythonx-backed) and to the LLM via
req_llm (Elixir-side, used by Gralkor.Distill and Gralkor.Interpret).
See test-trees/unit/gralkor-client-native_TEST_TREES.md.