update deps

- update rust to the latest version (1.80.1)
- remove structopt depedency and only use clap instead as structopt was
  relying on clap anyway, and the structopt features are now included in
  clap since clap v3 (structopt has entered maintenance mode / end of life).

The `release` target binary size has been reduced from 607K to 587K.

The next dependency update would be to switch the rust edition from "2021" to
"2024" when it will be supported (starting in october if all goes well).