Update s_region following tweakreg

[schlafly]

I think tweakreg currently updates only the image WCS but not the s_region. The s_region is used to determine the boundaries of the CCDs, e.g., in the MAST viewer, and we should update it when we update the WCS.

I think the WCS gets replaced here:
https://github.com/spacetelescope/romancal/blob/main/romancal/tweakreg/tweakreg_step.py#L273
but I think that's it.

Vaguely relatedly, we don't update other WCS keywords like ra/dec_ref, roll_ref. I don't think there is a good way for us to update those in the current scheme, though, and still be able to reproduce the WCS, so I don't think we should tackle that at present.