Update locked dependencies.
Use short-hand field patterns.

Fixes some warnings with latest Rust.
Don't use unpack for testing.

Unpack (the function) is going away soon.
Remove unpack usage in core.

Unpack is no more, and the deprecation warnings are gone.  Rejoice.
Use single-quotes for packing.

This brings the packer in line with the C++ version used in ury-playd.
Also, we now use .add() instead of .push_str(), amongst other
improvements.