feat(balance): mech speed updates, exempt mechs from monster speed/resilience settings

[chaosvolt]

Purpose of change

This aims to make mechs a bit less clunky for general use, in particular fixing an issue where making monsters slower overall has the annoying side effect of making mechs slower too.

Describe the solution

C++ changes:

1. In monstergenerator.cpp, updated MonsterGenerator::finalize_mtypes so that the world setting multipliers for monster speed and resilience aren't applied to mechs, making their speed and HP stay consistent regardless of world settings.

JSON changes:

1. Increased speed of lifter mechs from 50 to 100, making them on par with a baseline character speedwise for the player's convenience.
2. Increased speed of combat mechs from 65 to 125, to give them a bit more hustle to again make them worth using over just loading up in power armor.
3. And likewise, boosted scout mechs from 120 speed to 150, to have them stay the fastest vanilla mech.

Describe alternatives you've considered

1. Leaving the speed of scout mechs unchanged and only buffing combat mechs to 110 speed, to make for a more narrow progression in speed.
2. Changing other monsters to also be excluded from monster speed/resilience calcs. Maybe monsters in the wildlife category I guess, or we could JSONize it in the form of a monsterflag specifically for any exceptions we want to specify? Maybe we can do that in a follow-up and just focus on making mechs exempt for now.

Testing

1. Checked affected JSON for syntax and lint errors.
2. Compiled and load-tested.
3. Loaded in a world with default settings, spawned in a lifter mech, confirmed it shows as being as fast as I am.
4. Repeated this test in a world with monster speed set to 10%, confirmed lifter mech still shows as being as fast as me.
5. Spawned in a zombie runner to confirm it was showing as properly slowed way down.

Additional context

Checklist