allow for turning off fourier positions for experimental perceiver (i…

…sab-like) for @nleroy917

remove freq base from all perceiver variants

make sure variable lengthed sequences are dropped out correctly

add a structured dropout for incoming data being perceived, after see…

…ing PerAct paper use perceiver io successfully for robotics

add a structured dropout for incoming data being perceived, after see…

…ing PerAct paper use perceiver io successfully for robotics

fix experimental.py

fix a bug with weight tying across layers and number of self attentio…

…n transformer blocks > 1, thanks to @yuanmao

fix dropout in original perceiver

make it so perceiver io decoding queries can omit the batch dimension