fix(harness): consolidate duplicated math scoring into shared module #1090

Job	Run time
uv workspace (lock + sync + import smoke)	54s
Build (cmake + uv sync --extra megakernel)	18m 7s
GPU tests (self-hosted Radeon 8060S, gfx1151 / ROCm)	-1s
GPU tests (self-hosted RTX 3090, sm_86)	-1s
	18m 59s

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