Backends multi-node distributed compilaton

[FlorianDeconinck]

An enduring issue with the model right now is the incapacity to efficiently build at-scale. Every stencil takes a significant amount of time to build due to the well known under performance of nvcc. This coupled to the fact that the cube sphere means we have up to 9 different code path (following the placement of a rank on any given tile), this leads to build time up into the 3+ hrs.

A solution is to use distributed compilation on multi-node*. Using the new identify code path technique, that guarantees relocability we should be able to compile with 54 ranks and scale up to any layout.

Here's an outline of a solution:

• Rank 0 spins a file socket server - acting as a scheduler for everybody else
• When hitting FrozenStencil, the rank queries the server for stencil state
  • Build: stencil is not built - build it
  • Stub: stencil is being built - stub for now come back when execution is needed
  • Load: stencil is ready load it
• When a stencil needs to be executed, the rank queries the server until given the "Load" call

• Why not multithread? Because Python+ GIL = sad developer

[FlorianDeconinck]

This issue should also be the base for a full uprooting and refactor of the CompileConfig, distrubuted_caches, etc. and all build/load system that has been growing in multiple files in both Orchestrated and Stencil based system.

The build system should be the same for all execution - presenting an unify API to users to create workflow.