Distributed fields do not work with even-odd preconditioned Dirac operators

[GianlucaFuwa]

As title says.
Reasons are that, e.g., eo_site doesn't work on bulk sites and even if fixed, all dirac kernels would have to get bulk_sites as input,
Also, would be good to find a way to automatically determine halo_width and/or save on halo_width when possible (e.g. 1-hop operators unnecessarily getting halo_width 2 - to do this the whole iteration system would have to revamped though, so idk yet)