Deal with errors during compression

[edsko]

Compression is currently defined as

data Compression = Compression {
      compressionId :: CompressionId
    , compress :: Lazy.ByteString -> Lazy.ByteString
    , decompress :: Lazy.ByteString -> Lazy.ByteString
    }

The type of decompress should instead be

data Compression = Compression {
      compressionId :: CompressionId
    , compress :: Lazy.ByteString -> Lazy.ByteString
    , decompress :: Lazy.ByteString -> Either DecompresionFailure Lazy.ByteString
    }

And these decompression failures then need to propagate everywhere, and the specific instances of Compression (such as gzip) need to be modified.

[edsko]

Lowering the priority of this issue to low, since the probability that a peer sends us messages that have compression errors in them is very low.

If we implement this, we should think about whether the difficulty of streaming decompression whilst checking for errors is relevant or not (@FinleyMcIlwaine has some discussion of this issue at https://hackage.haskell.org/package/snappy-c-0.1.0/docs/Codec-Compression-SnappyC-Framed.html#v:decompressWithParams-39-).