air sumcheck: 'right-to-left' (lsb first) folding (no more bi-directional folding from the verifier's point of view)

[TomWambsgans]

• Keeping alsmost the same prover performance thanks to a locally bit-reversed representation of the multilinear polynomials, allowing to keep using SIMD in the first ≈ 10 rounds)
• folding lsb-first = padding-friendly, i.e. the cost of the AIR sumcheck is proportional to the 'useful' part of the columns (we don't pay for the final padding. In msb-first folding, after the first round, the padded part disappears, merged with the non-padded part.