Bump cast dependency and other misc stuff

[pali6]

Bump cast to 0.3 and criterion-plot to 0.6 (cast is a dependency of criterion-plot). The reasoning is that the currently used cast version depends on an outdated version of the rustc_version crate, which breaks on plenty of non-standard builds of the Rust toolchain. We use such a build of the toolchain internally and I'd like to prevent cargo-criterion from not compiling on it.
Also update Cargo.lock.
I wanted to run tests, but it turns out that one of the tests behaves incorrectly on Windows by hardcoding / path separators so I also fixed that.

[pali6]

I have not bumped other dependencies (toml, clap, simplelog and the three dev-dependencies) as these do not directly affect my issue. However, if you want I can expand the PR to bump those too.