don't swallow errors in the engine

There are many places in the engine, especially on the fuzzing thread, where exceptions are swallowed. We need to make sure exceptions are reported to be able to quickly diagnose errors.

This work item is opened to fix recently observed cases. For example:

    try:
        with open(grammar_path, 'r') as grammar:
            schema_json = json.load(grammar)
    except Exception as err:
        logger.write_to_main(f"Failed to process grammar file: {grammar_path}; {err!s}", print_to_console=True)
        sys.exit(-1)


except ValueError as err:
    logger.write_to_main(f"Failed to parse grammar file for examples: {err!s}", print_to_console=True)
    return False