Medical Vitals - Add SPO2

[BrettMayson]

When merged this pull request will:

• Adds a function to get oxygen density given weather conditions
• Adds an SPO2 simulation
  • Advanced fatigue recovery speed is influenced by SPO2
  • SPO2 decrease rate is influenced by demand for fatigue recovery
  • Heart rate is influenced by SPO2 and oxygen demand (fatigue recovery)
  • SPO2 increase rate is influenced by oxygen density, heart rate
  • Allows headgear and facewear to conditially supply oxygen

There are a lot of magic numbers, this is mostly an approximation as there is no way to properly simulate this without simulating the whole human.

Going to do more testing and maybe value tweaking, but I don't plan on adding anything more to this PR. I think #8929 should be fixed up and updated to use this system

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[BrettMayson]

My group is currently playing with the PR merged, problems with respawn and trying to fully heal. Also want more testing on HR.

Issues found

[johnb432]

@LinkIsGrim Don't you think it's slightly OP to reset oxygen demand when a unit is fully healed, especially if #9714 is going to considered?

[LinkIsGrim]

No. It's a full heal, and resetting oxygen demand to 0 won't change an/ae reserves. It will just be recalculated to an accurate value a few frames later anyway.

[johnb432]

My group is currently playing with the PR merged, problems with respawn and trying to fully heal. Also want more testing on HR.

Apart from that, what else needed fixing?

[BrettMayson]

Maybe some balancing, and we have a compatibilty issue with grad trenches currently, or rather their stamina bug

[BrettMayson]

Seems to be working great, no more passing our from a 30 second sprint

[LinkIsGrim]

Oxygen saturation will tend towards 100 on most maps, but the functionality is fine. I think we should get this merged and tweak the math as necessary.

[johnb432]

Do we want to merge this now or wait for another release?

[johnb432]

LGTM