CLI: Search upwards for Cargo.toml to detect --project-path

[bfops]

Several CLI subcommands (publish, build, generate, possibly others) attempt to determine whether the project is Rust or C# by looking for a Cargo.toml file in the current directory (or the --project-path if passed), and assume C# if the Cargo.toml is not found. This is a bad system and should be changed, but at the very least, they should search up for the Cargo.toml so that it's possible to run the commands from a subdirectory of a Rust project (e.g. in src/).