NESO Nektar++ shim composite capability

[jwscook]

We need to be able to detect whether particles are out of the grid

• in generality need to know which composite particle has gone through (NOT REQUIRED RIGHT NOW THOUGH)
• need to know if of f the end or if outside the outer "radial" boundary

N.B. The grid for September is a Cartesian approx of a cylinder. There are 3 composites: 1 each at the ends, and 1 for the "radial" boundary.

[jwscook]

Need to account for particles going through MPI boundary and then through a Composite in one timestep.

[jwscook]

Progress is being made

[jwscook]

Works on 1 rank, debugging on several ranks

[jwscook]

It works - PR exists and just needs merging.

[jwscook]

This is "roughly" working in 2D and works to the MAST-U mesh. Something is wrong with some mislabelled things in the mesh but will be fixed manually. This will be added as a test-asset.

[oparry-ukaea]

@JamesEdgeley has reviewed and encountered problems with NESO-Spack; @will-saunders-ukaea will check he's merged main.