Warn when the linted project contains a `rust-toolchain` or `rust-toolchain.toml` file

[smoelius]

I.e., warn when the user may encounter the problem described here: https://github.com/trailofbits/dylint/blob/master/docs/how_dylint_works.md#limitations

The warning should be suppressed when the file specifies the same toolchain the lint uses.

[smoelius]

Also, cargo dylint might run cargo --version in the directory being linted. If the command returns something unexpected, report that fact.

Thanks to @GrosQuildu for sharing this problem.