Make `Zlib` `Compressor` and `Decompressor` `~Copyable`

[gjcairo]

We have TODOs in grpc-swift-nio-transport to make the Compressor and Decompressor ~Copyable “when Swift 5.9+ is supported”. This is already true, so it should be done.

[glbrntt]

Marking as medium sized because I suspect this will bubble up to state machines which hold it.