Simplifies the script to automatically compile, run (60s), and generate
the coverage report in a single invocation. Removes the two-step --report
flag approach and adds quieter output with clear step markers.
Adds build_coverage.sh script that:
- Builds the simulation with GCC branch coverage instrumentation
- Supports --report flag to run simulation and generate lcov HTML report
- Uses 60 second timeout with SIGINT for graceful shutdown
Also adds SIGINT handler to simulation to exit cleanly and flush coverage data.