LearningSparse simulation (floating_pt and fixed_pt) fails with certain learning rules

[gkarray]

Describe the bug
LearningSparse simulation (floating_pt and fixed_pt) fails with certain learning rules.
My diagnostic is that scipy.csr_matrix cannot handle some of the operations executed by the LearningRuleAppliers.

To reproduce current behavior
Steps to reproduce the behavior:

1. When I run this code (add code or minimum test case) ...

def my_code():
    pass

2. I get this error ...

Error...

Expected behavior
A clear and concise description of what you expected to happen.

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Environment (please complete the following information):

• Device: [e.g. Laptop, Intel cloud]
• OS: [e.g. Linux]
• Lava version [e.g. 0.6.1]

Additional context
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