feat: Add per-node log level support via NodeOptions

[penww]

Add a log_level option to NodeOptions that allows setting the initial log severity for a node at construction time, enabling per-component log level customization in component containers.

Description

Fixes (#3091)

User could set log level for single node and component.

• Set component log_level with CLI:

ros2 component load /ComponentManager <PKG> <PLUGIN> --log-level debug

• Set component log_level with launch:

def generate_launch_description():
    return LaunchDescription([ComposableNodeContainer(
        name='component_demo_container',
        namespace='',
        package='rclcpp_components',
        executable='component_container',
        composable_node_descriptions=[
            ComposableNode(
                package='<PKG>',
                plugin='<PLUGIN>',
                log_level='DEBUG',  # component log level
            ),
        ],
        arguments=['--ros-args', '--log-level', 'DEBUG'],  # container log level
    )])

Is this user-facing behavior change?

No, the additional log level option is optional and default back to the current behavior.

Did you use Generative AI?

Partially with Claude Sonnet 4.6

Additional Information

Look at: #3091

[penww]

@alsora could you help to review this PR?

[penww]

It seems CI failed by other code, could you help to re-run CI? @jmachowinski

--- stderr: rclcpp                               
/opt/ros2_ws/src/ros2/rclcpp/rclcpp/src/rclcpp/subscription_base.cpp: In member function ‘bool rclcpp::SubscriptionBase::is_cft_supported() const’:
/opt/ros2_ws/src/ros2/rclcpp/rclcpp/src/rclcpp/subscription_base.cpp:486:10: error: ‘rcl_subscription_is_cft_supported’ was not declared in this scope; did you mean ‘rcl_subscription_is_cft_enabled’?
  486 |   return rcl_subscription_is_cft_supported(subscription_handle_.get());
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |          rcl_subscription_is_cft_enabled
gmake[2]: *** [CMakeFiles/rclcpp.dir/build.make:1292: CMakeFiles/rclcpp.dir/src/rclcpp/subscription_base.cpp.o] Error 1