Atom fire system.

[MistakeNot4892]

Description of changes

Copying this from #3435 due to a branch rename. Adds an atom-level fire system with the goal of replacing ZAS fires for most cases.

In summary:

• Atoms have a proc, get_flammable_material, which returns all constituent material that has a fuel value and ignites at or below the given temperature. This uses reagents by default and adds matter when it's an /obj.
• A new subsystem, SSfires, handles burning atoms as well as cross-turf spreading.

TODO

• [ ] Get temperature from fires working to an acceptable level.
• [ ] Move on-turf spreading onto SSfires as well as cross-turf.
• [ ] Convert mob fires to atom fires.
• [ ] Convert fire sources to atom fires.

Why and what will this PR improve

:fire:

Authorship

Myself.

Changelog

:cl: add: Atoms can now burn. Report bugs with fires on the issue tracker! /:cl: