15 math tests added across frustum and mat4 modules

[MichaelFisher1997]

Done. Created 2 test files with 15 tests total targeting engine/math:

frustum_tests.zig (8 tests):

• Frustum containsPoint — inside and behind-camera cases
• Frustum intersectsAABB — intersecting and fully-outside cases
• Frustum intersectsChunk — near and distant chunk cases
• Plane signedDistance and normalize

mat4_tests.zig (7 tests):

• Mat4 rotateX, rotateZ — 90° and 0° cases
• Mat4 lookAt — facing direction and length preservation
• Mat4 orthographic — matrix structure verification
• Mat4 perspectiveReverseZ — matrix structure
• Mat4 ptr — pointer validity

All tests pass (zig build test exits 0). No non-test source files modified.

Triggered by scheduled workflow

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