Function matrixShape

Computes the logical { outer, inner } shape of a matrix param from its dependsOn and dims — inner doubles as the minimum valid value for whichever ld* field it depends on. Returns null for non-matrix specs (no ld* in dependsOn).

• dependsOn has a trans* field and "k" → Level 3 matrix whose shape swaps between (dim1,k)/(k,dim1) with its own trans flag, where dim1 is whichever of "m"/"n" appears first in dependsOn — e.g. ["m","k", "lda","transA"] (sgemm's A) is (m,k)/(k,m); ["k","n","ldb","transB"] (sgemm's B) is (k,n)/(n,k); ["n","k","lda","trans"] (ssyrk's A, no separate m — its own n plays that role) is (n,k)/(k,n) — the array's own order carries the distinction, not the specific field/ld names, since a field name alone (e.g. "ldb") isn't enough — ssyr2k's B also depends on "ldb" but is (n,k)-shaped like an A, not (k,n)-shaped like sgemm's B.
• dependsOn has "m" and "n" (no trans) → plain matrix: m×n (row-major) or n×m (column-major) — sgemv/ssyr2/etc.'s A, sgemm's C.
• dependsOn has "n" alone → symmetric: square n×n (ssymv/ssyr's A).
• dependsOn has "side" (and "m"/"n") → symmetric whose order is picked by dims.side at read time — m ('left') or n ('right') — e.g. ssymm's A. Square either way, so layout doesn't affect the shape.

Shared by ndArrayLen (array sizing) and buildArb (fixtures, to chain ld* in [inner, inner+pad]) so the two never drift apart.