feat(kernel): skinny_matmul, dense small-N matmul for speculative verify widths - #30
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MLX's steel GEMM leaves the GEMV fast path at M >= 2 and runs small-N large-K shapes far below their bytes (router gates, indexer weight projections, hyper-connection mixes at speculative verify widths: 19-42us per call where the bytes cost 3-8us). One simdgroup per output column streams the w row coalesced holding all M row accumulators in registers, f32 accumulate, one round at the write. 4-8x per call at M in 2..16, parity with the stock GEMV at M=1. CPU eval mirrors the kernel semantics.
…garbage The factories short-circuited the Contiguous node on a build-time row_contiguous flags check, but flags of an unevaluated array are not meaningful yet (a transposed lazy view reports contiguous), so the kernels walked the wrong strides. Unconditional Contiguous node, which aliases zero-copy at eval when the input is already packed. Same class as the gather_qmm fix; moe_glu/route_shed sites still use the ternary on activation inputs that are contiguous products today.
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