Add Samsung SEF 3P plugin (JPEG SEFH/SEFT trailer and HEIC sefd box)

[DichenZhang1]

Summary

Adds the samsung_sef 3P metadata provider plugin supporting Samsung Extended Format (SEF) Motion Photos across both JPEG (container.trailer with SEFH/SEFT) and HEIC (heic.sefd box paired with mpvd).

Key Changes

• Plugin Implementation (lib/core/plugins/samsung_sef/):
  • samsung_sef_metadata.proto: Defines SamsungSefMetadata (sef_version, sef_entry_count, has_motion_photo_data, motion_photo_data_magic, video_offset, video_length, primary_image_timestamp_us, sef_keys).
  • SamsungSefProvider: Parses backward-indexed SEFH/SEFT directories (v106 and v107), extracts MotionPhoto_Data (0x0A30), strips 12-byte mpv2/mpv3 headers in JPEG trailers to expose the exact embedded MP4 stream, and resolves heic.sefd pointers to the mpvd box payload.
• Engine & Splitter Plumbing:
  • Passes HandlerOptions (disable_3p_plugins, enabled_3p_plugins) into MetadataEngine::Parse.
  • Updates JpegContainerSplitter to inspect the 32-byte EOF tail and adjust trailer_start to the earliest SEF record (sefh_offset - max_neg_offset) when SEFT is present.
  • Updates HeifContainerSplitter to emit heic.sefd blocks with associated mpvd bounds.
• Tests (samsung_sef_provider_test.cc):
  • Unit and end-to-end tests covering Identify, DecodeToSemantic, GetVideoInfo, IsMotionPhoto, SEF v106 (mpv2 & raw MP4) and v107 (mpv3), HEIC sefd+mpvd splitting, primary image/video extraction, HandlerOptions gating, and corrupted/overflow boundary safety.