Draft: Caching addon runner

Wishlist:

• Ability to either process live data (pass-through mode) or cache some trains to later do the same processing to them
• Ability to start building new cache while still processing old cache (two buffers, swap later)
• Load correction addons from entry points like correction devices
• Run correction addons
  • Load data to GPU first
  • Run "while data on GPU" hook
  • Get data off GPU
  • Run "after data is back in memory" hook
• Provide proper output schema
• Look more like a device
  • Monitor, provide geometry
  • Have, potentially, a list of fastSources
  • Imitate other device properties as needed (not well-defined, should improve API instead of assuming addons will inspect device schema / properties deeply)