message: nydus-image: do not allocate chunk index for duplicated chunks
  Do not allocate chunk index for duplicated chunks, so we could get
  a compact blob compression information array.
diff: @@ -634,11 +634,13 @@ impl StargzBuilder {
  let mut chunk_map = HashMap::new();
  for chunk in &mut blob_chunks {
  + if !chunk_map.contains_key(chunk.inner.id()) {
  let chunk_index = blob_ctx.alloc_chunk_index()?;
  chunk.inner.set_index(chunk_index);
  chunk_map.insert(chunk.inner.id(), chunk_index);
  blob_ctx.add_chunk_meta_info(&chunk.inner)?;
  }
  + }
  // Set blob index and inode digest for upper nodes
  let mut uncompressed_blob_size = 0u64;
  