Inside the static math class, the unqualified name `float3` resolves to
math's own `float3(float,float,float)` constructor-function first, not the
CultMath.float3 type, so `float3.zero` fails to compile there (CS0119). No
prior code in math.cs used the Type.zero static-field spelling from inside
math itself for this reason. Switched cellular's zero vectors to
`new float3(0.0f, 0.0f, 0.0f)`, which is unambiguous under `new`.
Found by the first ygg-verify.sh build/test run on 3eed434.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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