Implements FrameDecoder with five timing rules that mirror UDPSourceSession.cpp: FullArray (per-element time signal), FirstSample and LastSample (rate-spread from anchor), accumulated scalar with declared rate (forward-chain anchoring, immune to arrival jitter), and PACKET burst (backward-span from previous arrival). 9 new tests, 38 pass total. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>