Run `cargo fmt` before filing PR?

[lnicola]

Not sure if it's because rustfmt doesn't run on r-a downstream or if it runs with different settings, see rust-lang/rust-analyzer#20779.

[Kobzol]

Yeah I guess that could be useful. I wonder if we should just allow some general configuration of what to run after a pull, because e.g. miri does ./miri toolchain && ./miri fmt check ....