Tire force combining review

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I've been working on the physical tire model again.

Checked my integrals with wolframalpha.com and found/fixed two errors.

I think it is now good enough to be tested in vdrift, will start porting it to C++.

The physical model has a slip velocity dependency. The magic formulas don't model this at all, are captured at some fixed velocity. This dependency might cause issues with the ABS/TCS/AI implementation, as it shifts the ideal slip points. It will be interesting to see whether it breaks anything.