add: leaky_relu non-linearity

[dcbuild3r]

Add Leaky ReLU by rebasing from main

[alexander-camuto]

We also want to read in the leaky relu slope somewhere here; from the Onnx node.

[alexander-camuto]

Hey @dcbuild3r thanks for this its looking really good.

In terms of next steps:

• ensure non-linearity behaves as expected by generating an Onnx graph / input file for a graph with a single LeakyReLU op (with slope 0.05) and then running ezkl on it
• once it is working you can add that example to this repo and add the example to the tests/integration_tests.rs file.
• more broadly we probably want to think about how to generalize ingesting the slope parameter into the LeakyReLU function. It could just be item 2 of the scale array or something.
• concurrently we also need a way to load that parameter from the Onnx node. I've added a comment where it should probably happen in the code. Onnx / tract can be kind of fiddly and have inconsistent interfaces for loading parameters so lmk if you need help with that.