Fixes the easy stuff from: #22545
The only real balance change, dropped improvement per variable by 50%.
Should have been like this from the start, but I mistakenly assumed no
one would even reach close to the cap.
Makes repairs with welders go through .use_tool, fixes not needing
welding goggles and adds nice sparky visuals.
Much more robust handling of improvable variables, negatives don't break
improvement assignment now.
Fixes improvement cap, missed a *100 to convert from decimal to
percentage.
Fixes improvement potential being assigned to things that couldn't be
upgraded.
Fixes the Gatling mod upgrading fire delay (pretty useless on something
with a 3 second warmup)
Fixes the weapon analyzer print out showing completely incorrect
numbers.
Fixes the weapon analyzer eating your combitool and being
indestructible.
Gives some more feedback on why things can and can't be upgraded.
