Add Phasor layers/network capability

[kmheckel]

It would be awesome to implement the ability to train spiking phasor networks in Spyx. JAX has the ability to support complex-valued autodifferentiation, so this should be possible. Doing this would enable extremely fast training by eliminating recurrence when learning before converting to a recurrent architecture for inference.

https://arxiv.org/abs/2204.00507

[kmheckel]

This is tied to the implementation of latency based training tools/objectives. #21