A native session's messages went to ONNX Runtime's stdio logger, which is
nowhere once the app is launched from a menu — and what a provider says
while partitioning a graph (nodes taken, operators declined, a library that
failed to load) is most of what a failed rung tells you. Each session now
forwards them to `log` under the target `onnxruntime`: warnings always,
the runtime's info lines at `debug`, its verbose lines at `trace`.
dtourolle
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