QF8 Encoding: 1-bit sign + 7-bit u3.4 log₂ code + E8M0 block scale

The QF8 format encodes each value as a 1-bit sign and 7-bit u3.4 fixed-point log₂ code, with a shared E8M0 block exponent per 32 elements. Reconstruction: x̂ = (-1)^σ · s · 2^((c-64)/16). Effective cost: 8.25 bits/element. Provides 16 levels per octave across 8 octaves.