Improve Conv1D class to manage its own ring buffer

[sdatkinson]

Just a "little" task, but it'd be swell to take some of the TODOs around e.g. ring buffer handling and make good on them to rework the Conv1D class (cf https://github.com/sdatkinson/NeuralAmpModelerCore/blob/846968710a670d662b15e449edba852d747d748e/NAM/dsp.h#L169) and get rid of things like Buffer--things like Linear can be a DSP with one conv layer.