nx_sha256_sha384_coexist_kat_test.nx

nx_sha256_sha384_coexist_kat_test.nx -- regression KAT for the top-level `func blk_set_byte(...)` collision that silently corrupted SHA-256 whenever nx_sha384/nx_sha512 was also imported (2026-05-20, root cause of cert chain verify failures). Imports BOTH nx_sha256.nx and nx_sha512.nx (where sha384 lives), computes a SHA-256 over a known input, and asserts the digest matches the FIPS 180-4 KAT for SHA-256("abc"). expect_exit: 0 license_tier: ORIGINAL