A mesh is a named collection of devices arranged in a logical shape.
name is a string identifier for the mesh in the lowered program so that
sharding annotations can refer to a specific device topology without
embedding concrete device handles directly in the intermediate
representation.
shape is a tuple describing the logical layout of devices, where each
element is the size of a mesh dimension. For instance, a shape like
{2, 4} represents a 2x4 logical grid of devices.