feature/gpu updates

[jcelerier]

• serial: remove references to Qt QSerialPort
• graph: better support for feedback
• hash: migrate and uniformize around rapidhash
• disable_fpe: fix build with -ffast-math
• hash: replace wyhash wherever it is used
• geometry: add useful infrastructure features on our geometry type
• buffer: add usage denotation on buffer_spec
• dataflow: only advance in our position buffer if we actually managed to copy data
• geometry port: start introducing our scene graph nodes
• geometry: add useful attributes for per-instance stuff
• wip: proper point cloud support in scene