Fix issue 334

[PhilippPlank]

Changed calculation of wrapped_current.

Issue Number: #334

Objective of pull request: Fix subthr_dynamics() function for fixed point lif model so that neuron current wraps to opposite side of integer range rather than to 0.

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?

• Right now on integer overflow of current, the current wraps back around to 0

What is the new behavior?

• You'd expect the current to wrap around to -2^23 if the current is positively accumulating or +2^23 if accumulating negatively. That would be Loihi 1 behavior. Unclear about Loihi 2.

Does this introduce a breaking change?

• Yes
• No

Supplemental information

[GaboFGuerra]

Thanks Philipp, not sure if there should be a test added or affected by this.