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>
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