Hmm I have been working recently at a computer controlled enemy for etpro (based on some short code by wolfcam author) which does almost exactly what you say, but it's still beta, and since it's gpl I should give you the source as well , not to mention that I'd have to port it from Linux to Windows if you use win, but that wouldn't be hard. It should probably work for other mods as well, but I tested it only with etpro.

Since I wanted to play etpro again, I wanted to train with real etpro hitboxes and not bobots or similar sh*t, and my enemy strafes left-right and crouches to control spread, has a very good accuracy for even harder training, and also has an option for unlimited hp, or to give you unlimited hp. I use that together with an udp proxy to delay the packets to the server, so I can train with the same ping I have ingame, or even test how I hit with lower/higher pings or unsteady connections. (I know there is cl_packetdelay and stuff but I wanted a real ping not a simulated one)

Eventually I realized that the best thing is playing in real servers against real players. They might not be as highskilled as that computer one, and the training might not be as intensive, but real players are a better training because they are smart. And with all the tests I did I realized that etpro hitboxes are good with any ping, you just have to aim at the head, you have to blame only random bullets so there is nothing to really train, aim at the head and that's it. I tested it with slow timescales, antilag debug hitboxes, g_debugbullets and stuff. Etpro team did a very good job despite what all the stupid whiners around say, hitboxes are quite good, and antilag works, in these tests I had the same acc with pings ranging from 0 to 300+ and steady/unsteady pings.

I don't know if I will ever release this 'training opponent' because it's not much user friendly (and not very useful after all), but you could come close to something like that by starting a server with /devmap and doing /give health 10000, this way you have 10000 hp, then /give ammo (you can bind for example mouse1 "+attack;give ammo") if you do /god you will have no screenshakes, and that's not what you want