Draft: main/protobuf: upgrade to 29.3

@ncopa it turns out the latest protobuf v29.3 builds even with most of the patches from the v25.6 branch removed, they must have improved a lot of things upstream. I left in soversion.patch because it looked useful but the rest are no longer necessary. It's another option for you in case you want to update to the latest directly, although I'm not sure how this affects dependent packages.