Coloring support for symmetric pairwise operations, and extend HP tradequeues to other dimensionality and periodicities

[LonelyCat124]

At the moment, the HP tradequeues (3D periodic only also right now) doesn't support symmetric pairwise operations.

We can launch these in an index launched way using colored launches. There are a few ways to do this, and for now we're going to assume we don't have to worry about variable cutoff lengths, since these will already cause issues with tracing.

1 option (for complex colourings, i.e. when neighbour cutoff >> 1 cell width) is to do the colouring explicitly:

var color_region = region(cell_space.colors, int)
-- fill in the region 0, 1, 2, 3, etc. for each color
var color_partition = partition(color_region, ispace(int1d, 4))

for color = 0, 4 do
  var color_set = color_partition[color]
  __demand(__index_launch)
  for cell in color_set do
    ...

The color partition can probably be created during initialisation and just reused in the launchers.

Alternatively, for simple colourings, we can just do something simple like a checkerboard pattern without a color_partition:

var color_space = ispace(int2d, {3, 3})
for color in color_space do
  task1(p[{color.x*2, color.y*2 + 1}]) -- orange
end
for color in color_space do
  task2(p[{color.x*2 + 1, color.y*2 + 1}]) -- yellow
end