Anchored Stratification Arrays: designs and verification code

The two anchored stratification arrays constructed in the paper "Anchored Stratification Arrays" by R. C. Karunanayaka, together with self-contained Python programs that reconstruct them from the descriptions given in the paper and check every claim made there in exact integer arithmetic. Included are an ASA(16,7), an ASA(64,31) and an ASA(256,127), each attaining the bound of n/2 - 1 factors in n runs; a verification program covering the defining conditions, the orthogonality characterisation, the moment identities, the equality structure, the determinant identity behind the non-existence theorem, and the associated weighing matrix; the exhaustive signing search at GF(32), the monomial scan at GF(2^7) and GF(2^9), and the orbit-restricted search at GF(128) that produces the 256-run array; and the exhaustive search behind the remark on regular arrays. This version adds the ASA(256,127), the orbit-restricted search that produced it, and extends the verification program to cover all three arrays.