Return the length of the *input* vector, with three possible distance definitions:

#### Euclidian

The "ordinary" length of the vector: \( \sqrt{x^2+y^2+z^2} \)

#### Quadrance

Euclidian distance squared, which is cheaper to compute: \( x^2+y^2+z^2 \)

#### Manhattan

Measures distance following only axis-aligned directions, which is even cheaper to compute: \( \left|x\right|+\left|y\right|+\left|z\right| \)