[code-reflection] RFR: Updating the ONNX CNNTest

[Paul Sandoz]

On Wed, 5 Feb 2025 16:09:36 GMT, Adam Pocock <duke at openjdk.org> wrote:

> - Adds a Python script which trains a small LeNet style CNN on MNIST, exporting it to ONNX format.
> - Updates the CNNTest to match the trained CNN.
> - Added support for loading in the ONNX model, extracting the weights and saving them out in serialized Java records (this adds protobuf-java as a dependency along with the compiled ONNX protobuf).
> 
> The compiled ONNX protobuf is Apache 2.0 licensed, and the Python script is adapted from a PyTorch tutorial which is BSD licensed.

Marked as reviewed by psandoz (Lead).

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PR Review: https://git.openjdk.org/babylon/pull/307#pullrequestreview-2606936502