Function try_open_project_cache 

fn try_open_project_cache(
    root: &Path,
    profile: &str,
    profile_suffix: Option<&str>,
    variables: &BTreeMap<String, String>,
) -> Option<ProjectCache>

Try to open a long-lived ProjectCache (read-only SQLite connection).

Returns None if the database file doesn’t exist yet or can’t be opened.