Allocate all memories up-front

• Refactor memory allocation strategy for generated Hercules code
  • Allocate device memory up-front on calling a Hercules function
• Introduce HerculesRef types and HerculesRunner generated types for safe Rust interface
• Large refactor of GCM, includes base code for object allocation
• Enhancements for graphviz visualization

requested review from @aaronjc4

assigned to @rarbore2

changed the description

merged

mentioned in commit 1d2597f5