Make a zombie-flavored breather and cut spawns of them in meat lab

[kevingranade]

Summary

None

Purpose of change

Fixes #71349
As reported in the above issue, meat labs were suffering from pretty bad slowdown due in part to breather aggression and in part due to there just being way too many breathers.

Describe the solution

Made a clone of breathers and breather hubs that are exactly the same but on team zombie.
Except they also have a smaller radius, they spawn within 3 tiles of the hub instead of 4.
I also cut the base spawn rate of breather hubs in meat labs a lot, to 1/10 the previous number.
In aggregate that means there are about 1/20th as many breathers per area in the labs, and on top of that there are significantly fewer inter-faction checks happening because the vast majority of meat lab occupants are amalgamations, which are in the zombie faction.

Describe alternatives you've considered

There's a potential tradeoff of breather spawn radius vs number of breather hubs that spawn. This just gets the total numbers reigned in to a decent number.
I do think the faction shift is necessary, even with a hundred or so breathers that's still a lot of aggression checks getting triggered for no reason.

Testing

Found a meat lab with teleporting around, waited a few minutes to let the breather population stabilize, then ran the game under perf to capture a profile.
Checked with debug that the things are actually spawning.
Killed a hub to verify the on-death effect is kicking in.