Add tests for BMI effect on speed

[wapcaplet]

Summary

SUMMARY: Infrastructure "Add tests for BMI effect on speed"

Purpose of change

The effects of being underweight are poorly understood by both developers and some experienced players of the game, and deserve to be brought to light.

Describe the solution

Add a test case for player::kcal_speed_penalty testing and illustrating the effect of BMI (stored kcals) on overall speed:

• Normal weight (BMI 18.5 - 25) or heavier: No penalty
• Underweight (BMI 16 - 18): Reduces speed by 5% to 25%
• Emaciated, skeletal: Reduces speed by 31% to 90%

Describe alternatives you've considered

Keeping it a secret

Testing

tests/cata_test [bmi][speed]

Additional context

Discussed with other devs in discord; @KorGgenT and @kevingranade agreed there are no plans to reduce speed for being overweight, so I also removed a couple of comments in src/player.cpp to that effect.

[wapcaplet]

Clang-tidy spews a pile of errors that I cannot make sense of, and are totally unrelated to this PR:

/home/runner/work/Cataclysm-DDA/Cataclysm-DDA/src/faction.cpp:896:17: error: Called C++ object pointer is null [clang-analyzer-core.CallAndMessage,-warnings-as-errors]
            if( guy->has_companion_mission() ) {
                ^
/home/runner/work/Cataclysm-DDA/Cataclysm-DDA/src/faction.cpp:816:5: note: Loop condition is true.  Entering loop body
    while( true ) {
    ^
/home/runner/work/Cataclysm-DDA/Cataclysm-DDA/src/faction.cpp:833:9: note: Null pointer value stored to 'guy'
        guy = nullptr;
        ^

These appear to be related to changes added in #39753