HLS streaming nodes already have small FIFOs at i/o

[Transformation] Update FIFO insertion so the depth is set by the node attributes from the surrounding nodes

this will be replaced by a metadata_prop in the near future

set to a constant in the code for now, will move to attribute

let the user manage which layer uses what kind of mem resource
defaults to auto

let the user manage which layer uses what kind of mem resource
defaults to auto

build_dir = None creates a tmp dir that gets removed when the
PyVerilator object is destroyed