[gameplay] Adjust cavalry movement speed and melee attack range.
Nerf cavalry movement speed somewhat, by reducing walk speed and their run multiplier.
Further, following rP24798, units have a chance of going through their target when chasing them. This diff adjusts melee cavalry ranges from 4 to 6 to reduce the probability of that happening. The speed reduction also helps with this.
Refs #5936
Differential Revision: https://code.wildfiregames.com/D3483