Enable CPU-based period finding algorithms

[bfhealy]

In light of #499, we may not always want to offload feature generation to expanse. On smaller scales it may make more sense to run period-finding locally using CPU-based algorithms. These algorithms exist in ztfperiodic but are only partially implemented in scope. As part of efforts for #499, we could complete this task and enable fully local feature generation/inference as an alternative to expanse.