Bloat constraint for halo exchange boundaries

[krasow]

Solving a concern in cuNumeric.jl#130

This PR provides an initial implementation to the bloat constraint for halo exchanges on stencil applications.

Our initial results showcase a speedup due to more constrained data movement between independent partitions.

5-point stencil constraint benchmark
  backend: gpu
  grid: 1024 x 1024
  iterations/sample: 1000, samples: 3
  default alignment median: 4.6348 s
  bloat median:             2.5633 s
  bloat speedup:            1.808x
  alignment samples: [2.203563159, 4.903325947, 4.634762293]
  bloat samples:     [2.122456644, 2.563287343, 3.644802106]

Additionally add support for broadcast constraint.

Debugging and commits here were assisted by Claude Opus.