dash(s6): DIP-0027 asset-lock/unlock payload wire conformance KAT

[frstrtr]

Operator-decided scope (KAT assetlock): DIP-0027 asset-lock WIRE conformance as known-answer-tests — vector-driven serialization/parsing parity ONLY. No state machine (correctly shelved).

What

Adds 6 KATs to test_dash_conformance.cpp covering both DIP-0027 special-tx payloads the credit-pool balance scanner reads off the wire:

• CAssetLockPayload (type 8): single-output, two-output (+total_credit), empty-vector serialize KATs; parse inverse + trailing-garbage guard.
• CAssetUnlockPayload (type 9): fixed-layout serialize KAT (index/fee/requestedHeight + quorumHash + 96B BLS sig); parse inverse + trailing-garbage guard.

Non-circular

Expected hex computed OUT-OF-BAND with CPython (LE struct pack + Bitcoin CompactSize + raw sha256d/sig bytes), so pins do not derive from the C++ ::Serialize path under test. Parse cases feed the same out-of-band bytes straight into parse_assetlock_payload/parse_assetunlock_payload.

Isolation / verification

• Single-coin: src/impl/dash only; test-only (no production change).
• Linux x86_64 ctest: test_dash_conformance 29/29 green (was 23/29; +6).
• Target already in build.yml both --target lists; no CMake/workflow change.

Stacked on #138 (s6-cbtx-conformance); retarget to master once #138 lands.

[frstrtr]

Closing per operator: DIP-0027 asset-lock WIRE conformance is SHELVED (out of S6 scope, operator decision 2026-06-18). Branch + commits preserved (no delete) — reopen if it comes back into scope.