Make waveforms optional for `Spikes` API

[charlesbmi]

https://github.com/agencyenterprise/neural-data-simulator/issues/30

Introduction

User feedback:

I had a use case where I used the Spikes class to generate fake spikes so I could check the statistics of the fake vs real spikes. I didn’t need waveforms so factoring Spikes into something that doesn’t depend on waveforms (or only optionally does)... would be great.

This is a common use-case: the user may not want to use the compute-power to simulate full-bandwidth ephys signals and may only be interested in the spike times.

Changes

• Decompose Spikes class into a SpikeTimes-generator class (no waveforms) and a Waveforms-loading class (already defined)
• Updated pytest tests as needed

Behavior

• Works the same, based on pytest and running run_closed_loop locally/
• Developers can now instantiate a SpikeTimes generator class without defining Waveforms

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
...ural_data_simulator/scripts/run_ephys_generator.py	87.09% <ø> (ø)
src/neural_data_simulator/ephys_generator.py	74.92% <83.33%> (+0.08%)	:arrow_up:

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