Hello, I am using zstd-jni to write a pr(netty/netty#10422), and currently encounter 2 problems:

1. Zstd.decompressedSize() may return 0, is there any way to return the compressed block size of the data block
2. In reality, network packs data in frames. It's a frequent use-case that data arrive to the server in multiple chunks of a different length. The expected length should be taken from zstd header and decoder should wait until that data available before attempting to decompress. At present, a method is needed to determine whether the size of a complete compressed data block has been reached