`provekit/prover/src/whir_r1cs`: base-commit): drop this lift once zkWHIR v3 (`Basefield`) lets

[recmo]

On 2026-07-06 in 05de18e “Merge pull request #458 from worldfnd/sl/goldilocks-field-abstraction”:

base-commit): drop this lift once zkWHIR v3 (Basefield) lets
the ZK path commit base-field elements directly (V-stage).

        }

        // Pre-v3 WHIR ZK commits over a single field (`whir_zk::Config`
        // hardcodes `Identity<Ext>`), so lift the base witness to the
        // extension. The lift is a zero-cost identity for bn254.
        // TODO(base-commit): drop this lift once zkWHIR v3 (`Basefield`) lets
        // the ZK path commit base-field elements directly (V-stage).
        let embedding = <P::Embedding>::default();
        let mut padded_witness: Vec<Ext<P>> = embedding.map_vec(padded_witness);

        let blinding = if is_w1 {
            let g = generate_blinding_univariates::<Ext<P>>(self.m_0);

From provekit/prover/src/whir_r1cs.rs:108