[discussion] Support Advanced NAS Algorithms

Now we are using a custom IR (architecture + nn_config) to represent a candidate model, which may be insufficiently expressive, I think.

I think we should use mature IRs such as Relay IR or ONNX to represent the candidate model.

/cc @DeeperMind @andreyvelich

No file, test, or entry point is named. Start by locating the current architecture and nn_config custom IR, then compare its expressiveness with Relay IR and ONNX; done would require an agreed representation and a defined implementation plan for supporting advanced NAS algorithms.

Written by the indexing model from the issue text.