Explosion/dust animation is played when the projectile hits the ground. The visuals (eg. particle) for projectile hit animation can be defined in the unit actor with `attachpoint="projectile-hit"` (example attached in the diff):
```
art\actors\units\athenians\siege_rock.xml:
<prop actor="props/units/weapons/rock_explosion.xml" attachpoint="projectile-hit"/>
```
The length of the projectile hit animation can be defined in the Template with Decay/DelayTime.
A general purpose Visual Effect Manager (later used by the projectile hit and the continuous damage animations) will be designed and implemented in a separate ticket (if the audience agrees).