Optimization request for Sim::Unit::UpdateWeaponVectors

Right now UpdateWeaponVectors consume measurable amount of CPU when units are not in fight, here what can be done:
1. Use `for_mt_chunk` in `void CUnit::UpdateWeaponVectors()`. Sometimes like this.

```
for_mt_chunk(0, activeUnits.size(), [&](const int idx) {
auto unit = activeUnits[idx];
unit->UpdateWeaponVectors();
```

2. Add two checks to `void CUnit::UpdateWeaponVectors()`

`script->HaveAnimations()`
And another check that checking if unit changed own position.

Start at CUnit::UpdateWeaponVectors() and the activeUnits call site shown in the issue. Trace how weapon vectors are updated for units outside combat, then verify that the requested for_mt_chunk usage and both checks cover the intended idle cases; done means the update avoids unnecessary CPU work without breaking active-unit behavior.

Written by the indexing model from the issue text.