Experiment/recursive controller

[mwpb]

Create an ephemeral controller to run Tierkreis graphs. It can run a modified version of the sample graph and the QSCI time evolution graph on Fugaku.

• Create examples/numerical-worker that takes inputs and reads outputs from the filesystem. Create a launcher in examples/launchers that launches the numerical-worker.
• Create the NodeLocation model for identifying a particular run of a node in a graph.
• Test that the controller works by running the existing sample graph but with match statements removed. The controller does not support match statements as presently implemented because it would have to analyse the values contained therein. Loops are determined to break or continue using a struct instead.
• Create storage interface for managing the progress data of the graph. Create draft executor interface for running individual nodes.
• The tierkreis.controller.start:start function executes a node and then exits. It also takes care of finishing some nodes that don't require computation. The tierkreis.controller.resume:resume function recursively analyses the graph trying to find nodes that can be started. At the moment we just immediately execute startable nodes as we find them.
• (Try to get CI to pass.)