[gameplay] Fix chasing range cavalry

This fixes chasing, particularly chasing ranged cavalry.

• Standardise the range of melee cav to 4.
• Decreases the speed of ranged cavalry slightly to make melee cavalry a better counter & reduce the ability of ranged cavalry to dominate an area.
• Fix UnitMotion to better chase units, by increasing direct-range distance and making "from scratch" short paths recompute better paths (by increasing the search range).
• Gives some free rotation time for slight angles to units. Angles below 30° take no time to rotate towards. Chasing units that recomputed a lot of paths could be slowed down substantially by minute angle differences.

Fixes #5936

Differential Revision: https://code.wildfiregames.com/D3402