chore(whir_zk): clippy + signature cleanup post-pruned-NTT

Reviewer flagged that `f_hat_witness: &mut` in `ood_stir_and_rounds`,
`gamma_check`, and `prove_blinded_polynomial` is no longer accurate —
the partial-encode path never mutates the witness. Switch to `&` and
drop the now-redundant `&*` reborrows. Misleading `&mut` could mask
future bugs where the witness is unintentionally mutated.

Also applies the smaller clippy/fmt nits the reviewer surfaced:
- ntt_partial: allow(dead_code) (kept pub for external callers; the
  hot path uses ntt_partial_with_plan_into)
- PartialNttPlan::size: const fn
- ntt_partial_with_plan_into: allow(significant_drop_tightening); the
  roots-table RwLockReadGuard is intentionally held across all DIT
  stages, mirroring ntt_dispatch
- assertion comparison form: `> n` instead of `>= n + 1`
- cargo fmt

`cargo clippy -- -D warnings` is now clean; 155 lib tests still pass.

Author: shreyas-londhe

src/algebra/ntt/cooley_tukey.rs

@@ -370,6 +370,7 @@ impl<F: Field> NttEngine<F> {
     /// `O(size * log(size))` for a full NTT.
     ///
     /// `size` must be a power of two.
+    #[allow(dead_code)] // public single-shot entry; batched callers use the plan-based path
     pub fn ntt_partial(&self, values: &[F], size: usize, indices: &[usize]) -> Vec<F> {
         let plan = PartialNttPlan::new(size, indices);
         let mut out = vec![F::ZERO; indices.len()];
@@ -383,6 +384,7 @@ impl<F: Field> NttEngine<F> {
     ///
     /// Sharing a single plan across many NTTs with the same `(size, indices)`
     /// avoids re-running the O(size · log size) mask construction per call.
+    #[allow(clippy::significant_drop_tightening)] // roots guard intentionally held across DIT stages
     pub fn ntt_partial_with_plan_into(
         &self,
         values: &[F],
@@ -397,7 +399,7 @@ impl<F: Field> NttEngine<F> {
             return;
         }
         assert!(
-            out.len() >= (indices.len() - 1) * stride + 1,
+            out.len() > (indices.len() - 1) * stride,
             "output buffer too small for stride"
         );
         if size == 1 {
@@ -507,7 +509,7 @@ impl PartialNttPlan {
         }
     }
 
-    pub fn size(&self) -> usize {
+    pub const fn size(&self) -> usize {
         self.size
     }
 

src/protocols/whir_zk/prover.rs

@@ -327,7 +327,7 @@ where
         alpha_coeffs: &[F],
         rho: F,
         folding_randomness: MultilinearPoint<F>,
-        f_hat_witness: &mut irs_commit::Witness<F, F>,
+        f_hat_witness: &irs_commit::Witness<F, F>,
         f_hat_polys: &[Vec<F>],
         masking_polys: &[Vec<F>],
         g_polys: &[Vec<F>],
@@ -353,7 +353,7 @@ where
             .open_from_coeffs(
                 self.prover_state,
                 &[&f_hat_refs],
-                &[&*f_hat_witness],
+                &[f_hat_witness],
             );
 
         let r_bar = folding_randomness.0;
@@ -454,7 +454,7 @@ where
     /// codeword matrix is never materialised.
     fn gamma_check(
         &mut self,
-        f_hat_witness: &mut irs_commit::Witness<F, F>,
+        f_hat_witness: &irs_commit::Witness<F, F>,
         f_hat_polys: &[Vec<F>],
         masking_coeffs_all: &[Vec<F>],
         g_i_coeffs: &[Vec<F>],
@@ -474,7 +474,7 @@ where
             .open_at_indices_from_coeffs(
                 self.prover_state,
                 &[&f_hat_refs],
-                &[&*f_hat_witness],
+                &[f_hat_witness],
                 &gamma_f_hat_indices,
             );
 
@@ -498,7 +498,7 @@ impl<F: FftField> Config<F> {
         &self,
         prover_state: &mut ProverState<H, R>,
         vectors: Vec<Cow<'_, [F]>>,
-        f_hat_witness: &mut irs_commit::Witness<F, F>,
+        f_hat_witness: &irs_commit::Witness<F, F>,
         f_hat_polys: &[Vec<F>],
         masking_polys: &[Vec<F>],
         g_polys: &[Vec<F>],
@@ -696,7 +696,7 @@ impl<F: FftField> Config<F> {
         Hash: ProverMessage<[H::U]>,
     {
         let Witness {
-            mut f_hat_witness,
+            f_hat_witness,
             mut blinding_poly_witness,
             f_hat_polys,
             secrets,
@@ -713,7 +713,7 @@ impl<F: FftField> Config<F> {
         let blinded = self.prove_blinded_polynomial(
             prover_state,
             vectors,
-            &mut f_hat_witness,
+            &f_hat_witness,
             &f_hat_polys,
             &secrets.masking_polys,
             &secrets.g_polys,