Bummer. Somebody must have worked hard at that. With modern ammo, bore corrosion usually isn't an issue. I've seen 10/22's that have gone decades without a cleaning and the bore shines right up. Perhaps a liner might be the answer?
Shoot it first, and run at least
100 rounds of lubed lead ammo through it to see how it shoots- then clean it as normal, not OCD clean, and shoot at least 100 through it again to see what you have; it might do surprisingly well & not need a liner.
As I said in a prior post, I've been using borescopes going back 20 years, rather consistently over the last 10 years. The images that I achieve through my medical grade borescopes would blow your mind, unfortunately they are not amenable to digital photographs because you have to use a surgical eyepiece, but the magnification and image quality are outstanding. I have scopes at different angulation's for seeing and magnifying the directly adjacent bore wall, viewing partially down the bore, and wide angle long view. The only way that I could produce postable images with them would be to bring home the Uber expensive OR video imaging equipment that belongs nowhere near my garage, LOL.
I can tell you with 100% confidence that what you see in a borescope does NOT always correlate with stellar accuracy on the line.
I would not worry overmuch about getting all of the fouling out of the pits after this cleaning marathon. They are going to fill back up every time you shoot it, and if you are to OCD about cleaning the pits out every time, especially if you use JB repeatedly, your problem will not be fouling, it will be wear & tear from over cleaning. I get that you want it 100% clean this time, and I say go for it, this has been very instructive for us all to watch. Once you've seasoned it again, I would only clean to see shiny lands and grooves, and leave the pits filled moving forward. In the early part of this thread, I was against using JB for a reason - as JDWinCO astutely stated, JB is an abrasive on par with Jewelers rougeand while shiny looks
good in a borescope, you are
removing metal. Get it clean, then shoot it with the knowledge that they have filled with lube and carbon, possibly a little bit of lead, but none of the corrosive stuff that created the damage in the first place. If you go back at it to clean the pits every time with JB, sooner or later I would bet you a new barrel that accuracy will fall off. Obviously, if you get it clean and shoot it and you have a 12 gauge pattern, a liner makes all the sense in the world.
Just my little old 2¢, FWIW