Add tests for frostbite threshold.

[kevingranade]

Is your feature request related to a problem? Please describe.
A user pointed out a potential problem with how we handle frostbite, innthat frostbite evidently does not occur in ambient temperatures above 28F.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4923033/

Describe the solution you'd like
With such a clear threshold, I'd like to add a test that places a NPC in an environment either above or below this threshold (with various wind conditions) and assert they do or do nor develop frostbite.

If course, once this test is established code should be adjusted to make it pass.

[stale]

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