Derive Macro orzir_macros::RegionInterface

#[derive(RegionInterface)]
{
    // Attributes available to this derive:
    #[region]
}

Implement the RegionInterface for the given struct.

For the region interface, the #[region] attribute is used to specify the region field of the struct.

There are currently two ways to specify these fields:

1. Using the #[region(n)] where n is the index of the field.
2. Using the #[region(...)], which means the field is a vector of the regions.

The type of the fields should be ArenaPtr<Region> or Vec<ArenaPtr<Region>>.