Pretty fast, pretty random, endless, seekable #golang Reader: https://pkg.go.dev/github.com/minio/pkg/[email protected]/rng#Reader

(16KB internal block of random data, xor with 32B value based on offset ⊕ per instance value)

Made for benchmarks, not crypto, it is trivially predictable. ~20GB/s with Go single core. ~60GB/s with amd64 asm.