[WIP] ONNX demo

[superlopuh]

This Draft PR tracks all the changes necessary to lower an ONNX graph that adds two tensors to linalg.generic representation. The objective is to bring the diff in xDSL down to 0 and then close this pull request. I'll comment on the bits of code with suggestions for how to get things in, would love some help from @kayode-gif and @alecerio who already have experience with ONNX.

pip install -e ".[extras,onnx]"
marimo edit onnx-frontend.py

Remaining tasks:

• add callable support in the interpreter and handle registers in calling convention to fix failing test
• merge sub lowering
• merge alloc lowering

[superlopuh]

All the functionality is now merged to either the ONNX notebook or the one going from linalg to snitch, closing!

[tobiasgrosser]

Lovely. Thank you!