Platform-independent SIMD in Go

Go is getting portable SIMD. Go 1.26 shipped architecture-specific APIs for amd64; Go 1.27 adds a simd package that covers AVX, AVX2, AVX512, arm64 NEON and WebAssembly behind one interface, with emulation as the fallback everywhere else. Still gated behind GOEXPERIMENT=simd, and there is no cross-lane sum yet - ReduceSum lands in the next release. Worth a look if you have been hand-writing assembly for hot loops.