Separate `check_model_inputs` into `capture_outputs` and `merge_with_config_defaults` + ensure correctness (#43862)
* start
* switch imports everywhere
* simplify
* fix
* latest model
* add test
* improve test
* fix
* fix
* fix
* oupsi
* doc
* better test
* fix a few
* fix
* more elegant fix
* finalize fixing output capturing layers
* fix all finally
* and the last nit
* damn the test value was plainly wrong