Adjust rarity of mechs in finales, fix a spawn

[chaosvolt]

Summary

SUMMARY: Balance "Mechs in lab finales won't fail to spawn, fix one case of spawning in a wall"

Purpose of change

During Thelonestander's BN stream today he finally ran into a mech lab finale, rare as those are, only to find that it had mech containment with no mech. Given these are fairly rare, burn up fairly rare power cells, and could use some improvements in the future anyway.

Turns out it was not only not a 100% spawn rate, but also that particular variant was set to spawn in a wall, most likely bugging it out.

Describe the solution

1. Fixed broken spawn of recon mech in one lab finale variant.
2. Set spawn changes of mechs in lab finales to 100%, checked the rest will all spawn in actually available space.

Describe alternatives you've considered

1. The spawn rate could possibly stay low (or maybe elevated but not 100%) for the lifting mech variants, because those two finales have a nanofab and the phase immersion stuff respectively. In contrast, the recon mech finale has just a keg of mutagen going for it, while the combat mech variant is nearly empty except for a single shot of mutation or more rarely smart shot.
2. Putting this off until he's actually done with the stream.

Testing

Checked affected file for syntax and lint errors.

Additional context