Measure critical function coverage

Measure code coverage targeting critical functions at 100%

When you must enforce 100% coverage on safety-critical functions (tree operations)

• · crate_name (default: outl-core)

• · total_coverage_percent
• · critical_function_coverage (do_op, undo_op, apply_op, creates_cycle)
• · missing_lines_report

• · cargo llvm-cov
• · cargo install

Rust project with Cargo; cargo llvm-cov not required (auto-installs)

• · cargo llvm-cov installation fails
• · Coverage < 100% on critical functions

• · Names specific functions (do_op, undo_op, apply_op, creates_cycle)
• · Shows missing-line details
• · Reports total + critical separately