GetRail handle tuple output

[JAG-UK]

The ABI for GetRail returns a tuple, not a struct, so unpack tuple before interpreting it

[JAG-UK]

This addresses issue #8 and it Works On My Computer with real rails on Calib (specifically 14108 on https://pay.filecoin.cloud/calibration/rails).

Looking at the ABI I think this was simply a bug and we don't need to handle the originally-implied unpack-straight-to-struct case but if I'm wrong let me know and I'll add the additional safety/testing.

[JAG-UK]

Also I notice that devnet has been deleted from the generated constants here. That's not a deliberate act of sabotage on my part: I just ran the command the CI told me to and this is what it did (probably because I don't have a devnet on this machine). Hope that's OK, again LMK what I can do to fix it if needed.

[parkan]

@JAG-UK thanks for the patch, in fact your approach of not checking in the devnet is probably more correct than what we were doing previously, which was sloppily checking in a non-CREATE2'd address which is useless to have in repo and breaks the verify-address test