Recurrent netx save and load

[timcheck]

Issue Number: #327

Objective of pull request: As a user, I want to be able to save and load dense recurrent networks from lava-dl into lava.

Pull request checklist

Your PR fulfills the following requirements:

• 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)
• 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
• Other (please describe):

What is the current behavior?

Cannot save/load recurrent network with NetX.

What is the new behavior?

A new hdf5 layer category for dense recurrent layers allows saving recurrent networks to an hdf5 file.

NetX can load into Lava a recurrent network from an hdf5 file.

A unit test shows example usage. An example 2-layer 5-neuron dense recurrent network is created in Lava-dl, saved to a hdf5 file, and loaded into Lava from the hdf5 file. The network is run in both Lava-dl and Lava on an example input to confirm matching activity level within an error margin of 2%.

Does this introduce a breaking change?

• Yes
• No

[bamsumit]

@timcheck all looks good. Please convert the example to an unittest as discussed.

[timcheck]

Thanks @bamsumit, I converted the example to a unittest.

[bamsumit]

@timcheck Looks good to me. Thanks for doing this.