Function find_project_root 

pub fn find_project_root(cwd: Option<&Path>) -> Result<PathBuf>

Returns the root path to set for the project root.

Traverse the dir tree up and look for a foundry.toml file starting at the given path or cwd, but only until the root dir of the current repo so that:

-- foundry.toml

-- repo
  |__ .git
  |__sub
     |__ [given_path | cwd]

will still detect repo as root.

Returns repo or cwd if no foundry.toml is found in the tree.

Returns an error if:

• cwd is Some and is not a valid directory;
• cwd is None and the std::env::current_dir call fails.