This PR adds temperature based coloring for atmos gas meters and freezers.
These values are based on the BODYTEMP icon warnings that you get when a room is too hot or too cold. There is also some minor code improvements where some of the icon heat and cold warnings were hardcoded values. I made this a constant in the __DEFINES.atmospherics.dm file that you can see below. These values have been applied to air alarms, thermomachines, gas meters, and species code.
This is a QoL update for atmos tech nerds. Instead of having to manually examine a gas meter or use an analyzer to determine what temperature is in the pipes you can rely on the colored icons to communicate that information rapidly. This should also help prevent harmful gas leaks where a person unwrenches a pipe without realizing there is hot gas inside it. And you should be able to troubleshoot a delaming SM faster and easier with these colors.
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