CLSAG_GG generation and verification with flat-buffer ring marshalling.
Cofactor helpers (PointMul8/PointDiv8) for 1/8 premultiplication handling.
CLSAG_GGX and CLSAG_GGXXG verify-only bindings (GGX sig size tests).
Bulletproofs+, BGE, and Zarcanum verification stubs — implementation
deferred to Phase 4 when RPC provides real on-chain proof data.
19 tests pass, 3 skipped (proof stubs), all clean with -race.
Co-Authored-By: Charon <charon@lethean.io>
Standard signature sign/verify round-trip with negative tests (wrong key,
wrong message). Ring signature (NLSAG) uses flat buffer C API to avoid
double-pointer indirection across CGo boundary. Round-trip with 4-member
ring and wrong-message negative test. All 15 tests pass with race detector.
Co-Authored-By: Charon <charon@lethean.io>
