FIX: Allocate row_ics with the correct nnz length in SPMatrix::new

`SPMatrix::new(row, col, nnz)` initialised `row_ics` with
`vec![0usize, nnz]` (a literal two-element vector `[0, nnz]`) instead
of `vec![0usize; nnz]` (an `nnz`-length zeroed vector). Anything that
allocated a fresh `SPMatrix` for in-place writes - most importantly
`SPMatrix::transpose` - then panicked with
`index out of bounds: the len is 2 but the index is K` on any matrix
with more than two non-zeros.

The bug surfaced while wiring the sparse-transpose path into
`examples/clippy_verify` during the Phase 2 clippy refactor; the test
was kept disabled at the time and noted in the commit log of 2f33cb2.

Fix the single-character typo and re-enable the sparse section of the
determinism oracle, asserting both a hashed transpose result and a
double-transpose round-trip on two distinct matrices. Verified
separately that the new `transpose().to_dense()` agrees element-wise
with the dense `Matrix::transpose` on the same input.

Author: Axect

examples/clippy_verify.rs

@@ -220,14 +220,18 @@ fn check_polynomial() {
 }
 
 fn check_sparse() {
-    // SPMatrix transpose (sparse.rs:97, 102) - skipped until the
-    // `SPMatrix::new` `row_ics` vector-length bug is fixed (line 30
-    // uses `vec![0usize, nnz]` where it should be `vec![0usize; nnz]`).
-    // Without that fix `transpose()` panics with index-out-of-bounds on
-    // any non-trivial matrix. The loops will still be re-checked via
-    // the regular `cargo test` suite once the underlying bug is
-    // addressed.
-    let _ = SPMatrix::from_dense; // keep the import alive
+    // SPMatrix transpose (sparse.rs:97, 102)
+    let m = ml_matrix("1 0 2 0; 0 3 0 4; 5 0 0 6; 0 7 8 0");
+    let sp: SPMatrix = SPMatrix::from_dense(&m);
+    let spt: SPMatrix = sp.transpose();
+    let recovered = spt.to_dense();
+    print_kv("sparse transpose hash", hash_matrix(&recovered));
+    // Also exercise a non-square shape and verify double-transpose
+    // returns the original.
+    let m2 = ml_matrix("1 0 0; 0 2 3; 4 0 5; 0 6 0");
+    let sp2: SPMatrix = SPMatrix::from_dense(&m2);
+    let sp2tt = sp2.transpose().transpose().to_dense();
+    print_kv("sparse round-trip hash", hash_matrix(&sp2tt));
 }
 
 fn check_useful() {

src/structure/sparse.rs

@@ -27,7 +27,7 @@ impl SPMatrix {
             col,
             nnz,
             col_ptr: vec![0usize; col + 1],
-            row_ics: vec![0usize, nnz],
+            row_ics: vec![0usize; nnz],
             data: vec![0f64; nnz],
         }
     }