Function measure_rust 

pub fn measure_rust(
    root: &Path,
    thresholds: RustThresholds,
    ignore: &[String],
    features: &[String],
) -> Result<Outcome>

Run the unit suite under cargo llvm-cov in root and check it against thresholds.

Shells out to cargo llvm-cov --lib --json --summary-only, omitting every path in ignore from the denominator (a single --ignore-filename-regex), then evaluates the export. ignore holds the coverage-rule exemptions resolved from config, as root-relative paths; features the [rust] features list to enable on the run (#266). cargo-llvm-cov must be installed.