Add per composable node log_level support

[penww]

Description

Fixes # (ros2/rclcpp#3091)

Is this user-facing behavior change?

No, this change add new parameter for ComposableNode, not affect the existing functions.

Did you use Generative AI?

Yes, partially with Claude Sonnet 4.6.

Additional Information

Example for per component log level feature enabled:

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', 'INFO'],  # container log level
    )])

Related PR: ros2/rclcpp#3092, ros2/ros2cli#1212

[fujitatomoya]

test would be ideal too.

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[penww]

Hi @fujitatomoya, thank you for the review. I've fixed the reported issues and updated the PR accordingly. I'd appreciate it if you could take another look.