Port the source tree's own iceberg ctime_tests block (guarded by
ENABLE_MODULE_ICEBERG, after the chilldkg block): a 3-of-5 group run
through shares_gen, a share serialize/parse roundtrip,
share_cache_create (with a CHECKMEM_CHECK proving the cache holds no
secrets), pubshare_gen, pubkey_agg, nonce_gen, nonce_agg and
partial_sign, with share secrets undefined and all protocol outputs
defined, following the frost/chilldkg annotation style.
Both memory checkers pass with zero new declassifies needed -- the
module's constant-time layering (vpss variable-time but secret-free,
scalar_poly keeping secrets away from inversions) was already in
place. Verified: valgrind ./ctime_tests exits 0, and the clang
MemorySanitizer build exits 0 (with the chilldkg block unaffected).
8c4bf548ed