87fb1595c968508e12301f88ecce721462b0e1c3
Add #[cfg(test)] coverage for src/codec/opus_impl.rs: encode→decode round-trip shape + signal-energy survival, decoded duration follows the packet, and the key regression guard — decode(None)/decode(Some(&[])) conceals exactly frame_samples per channel (960 mono / 1920 stereo), pinning the previously-fixed 120ms-burst PLC sizing bug. Tests-only; no production behavior change. Implemented by Gemini (junior implementer), reviewed and verified by senior (cargo build + clippy --all-targets + cargo test all green). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>