Binary compression support

I'd like to be able to use [UPX](https://github.com/upx/upx) for compressing binaries, since they can get my bins to a pretty small size.

Start by tracing cargo-dist's binary packaging and release flow to identify where an optional UPX compression step would fit. Confirm how UPX should be configured and what platforms or binaries it should affect; done means compressed binaries are produced reliably without breaking packaging.

Written by the indexing model from the issue text.