Remove dependency on core-io

The dependency on core-io means that the DCP client is incompatible with SDK 3. By removing the dependency on core-io, we the DCP client is made compatible with both SDK 2 and SDK 3.

As part of this change, the Netty and Jackson artifacts that were previously shaded into core-io 1.x will be shaded into the DCP client under a different package (so as not to conflict with the versions in core-io 1.x if SDK 2 is present).

This will be a breaking change, because the Netty ByteBufs are exposed as part of the DCP client's "public" low level API, and these ByteBufs will now be in a different package. In most cases a simple search & replace on the package name will be all that's needed to update consumer code with the new package name.