Simplify backend dependencies

[CodyCBakerPhD]

Build tests just started failing due to a new hidden library in matplotlib, which we shouldn't even need as far as I know to run GUIDE (I tried removing locally and ran through a bunch of pipelines, including tutorial generation, and everything worked fine)

I think spikeinterface[qualitymetrics] in neuroconv[testing] (a part of neuroconv[full]) might be the source of that, so testing if this simplifies things

In the same spirit, there is no reason to bundle pytest or pytest-cov with our actual official build releases, so I'm suggesting only installing it in the CI where it is needed to run tests

[CodyCBakerPhD]

Well I still have no idea where matplotlib is being installed from out of that, but I still think trimming the testing requirements out of package setup for GUIDE is in our best interest for everything outside of CI