MNIST Inference Tutorial using netx

[R-Gaurav]

Issue Number: #849

Objective of pull request: Contributing an inference tutorial on classifying MNIST using netx (by loading a trained slayer-network)

Pull request checklist

Your PR fulfills the following requirements:

• [x] Issue created that explains the change and why it's needed
• [ ] Tests are part of the PR (for bug fixes / features)
• [ ] Docs reviewed and added / updated if needed (for bug fixes / features)
• [x] PR conforms to Coding Conventions
• [ ] PR applys BSD 3-clause or LGPL2.1+ Licenses to all code files
• [ ] Lint (flakeheaven lint src/lava tests/) and (bandit -r src/lava/.) pass locally
• [ ] Build tests (pytest) passes locally

Pull request type

Please check your PR type:

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation changes
• [x] Other (please describe): Contributing a tutorial in lava-dl/tutorials/lava/lib/dl/netx/mnist

What is the current behavior?

• N/A

What is the new behavior?

• N/A

Does this introduce a breaking change?

• [ ] Yes
• [x] No

Supplemental information

An extended tutorial on training and inference both exists here.

[R-Gaurav]

Thank you for reviewing @bamsumit ! I have resolved your comment, as well as freshly evaluated the run.ipynb on CPU and Loihi-2.

[R-Gaurav]

Thank you @bamsumit for approving and merging :)