Streams are streams — they take impl Read, not Read+Seek or File.
- MkvStream::open takes impl Read (was Read+Seek)
- EBML element skipping uses skip_bytes() instead of seek(Current)
- Byte position tracking uses remaining-bytes counter, not stream_position()
- Removed file_size from open (progress is CLI concern)
- M2tsStream::open takes impl Read (was Read+Seek)
- Buffers first 1MB for FMKV header / PMT scan
- Uses chain reader (buffered head + rest) for sequential reading
- Duration unknown without seeking (0.0) — CLI can set from metadata
- Removed ReadSeek trait (no longer needed)
- WriteSeek kept (MKV muxer container format requires seeking internally)