[FEA] Optionally inform users when a Polars query falls back to the CPU

[beckernick]

Some Polars query plans won't be able to execute on the GPU, so they'll fall back to the CPU during execution.

We should enable users to opt-in to informative logging when this happens, perhaps by hooking into the Config logging verbosity controls.

[beckernick]

Discussed offline. Will try to hook into Polars verbose logging.