Improve CI workflow

[FantasyTeddy]

This is the implementation of the changes discussed in #311:

• Extracting the cargo fmt and cargo clippy steps into their own jobs.
  • @grtcdr: What do you think? Is this OK, or should we combine the two jobs?
• Fail clippy on warnings (required some minor code changes).
• Execute the "Test" and "Doctor" change on all platforms that support it.

Additionally, I removed the strip variable from the matrix, because it was never used.

[FantasyTeddy]

The "GNU/Linux x86_64 (x86_64-unknown-linux-gnu)" job seems to fail the "Doctor" stage because of an actual bug in libmacchina: https://github.com/Macchina-CLI/libmacchina/blob/main/src/linux/mod.rs#L831

[grtcdr]

This looks good to me, let's merge :)

I've added a safeguard to stop the program from crashing on Linux in Macchina-CLI/libmacchina@30abf25.