Rename n_input_pixels back to input_pixels for compatibility with models trained in old versions of the package

[OldLipe]

To ensure compatibility with models trained in previous versions of the package, it is required to rename the n_input_pixels parameter in the .check_processed_values function back to input_pixels. Users attempting to use version 1.5.0 encounter errors due to this change. Reverting the parameter name will allow seamless use of older models with the current version.