feat(stark): MMCS-style batched composition poly commitment

All tables compute composition polys in parallel, then commit into
one shared Merkle tree. Restructures Rounds 2-4:
1. Per-table parallel: reconstruct Round1, sample beta, compute composition
2. Shared: batch all composition parts into one tree
3. Per-table parallel: append shared root to forked transcript, Rounds 3-4

Adds comp_col_offset/comp_col_count to StarkProof for per-table
extraction from batched openings. FRI still per-table (next commit).

Author: diegokingston

crypto/stark/src/proof/stark.rs

@@ -62,6 +62,11 @@ pub struct StarkProof<F: IsSubFieldOf<E>, E: IsField, PI> {
     pub trace_ood_evaluations: Table<E>,
     // Commitments to Hᵢ
     pub composition_poly_root: Commitment,
+    // This table's starting column index in the batched composition tree.
+    // The verifier uses this to extract per-table columns from the full batched row.
+    pub comp_col_offset: usize,
+    // Number of this table's composition poly parts in the batched composition tree.
+    pub comp_col_count: usize,
     // Hᵢ(z^N)
     pub composition_poly_parts_ood_evaluation: Vec<FieldElement<E>>,
     // [pₖ]