Probe transform and decoders

Can now probe `transform` and `decoders`. Changed some of the learning tests to use these probes to ensure that some kind of weight changes are happening. Check out the plots produced by these tests, they're kind of interesting!
Makes sense! While trying this out to see what it looks like, I hit a bug, as we're now applying a synapse to a `(2, n_neurons)` signal. I think what I'll do is use an unrolled view in the synapse calculation... sounds like the right resolution?