Mark rclcpp::Clock::now() as const

[sloretz]

I think now() can be marked as const. All it does is call rcl_clock_get_now() which doesn't look like it modifies the clock to me.

• When get_now is rcl_get_ros_time: https://github.com/ros2/rcl/blob/e4f7e1367dfda83d3e309397f9201642ebe38618/rcl/src/rcl/time.c#L65-L73
• When get_now is rcl_get_system_time: https://github.com/ros2/rcl/blob/e4f7e1367dfda83d3e309397f9201642ebe38618/rcl/src/rcl/time.c#L44-L48
• When get_now is rcl_get_steady_time: https://github.com/ros2/rcl/blob/e4f7e1367dfda83d3e309397f9201642ebe38618/rcl/src/rcl/time.c#L36-L40

[sloretz]

CI (build: --packages-above-and-dependencies rclcpp test: --packages-select rclcpp)

• Linux edit: infra fail - auto reran as
• Linux-aarch64
• Windows edit: infra fail - auto reran a few times, failing for more infra issues, manual re-run:

[clalancette]

Seems reasonable to me with green CI (though I think we should run tests with --packages-above rclcpp, just to make sure no downstream packages have a problem with this).

[sloretz]

though I think we should run tests with --packages-above rclcpp, just to make sure no downstream packages have a problem with this

What might happen downstream at run time that needs to be tested?

[clalancette]

What might happen downstream at run time that needs to be tested?

Actually, that's a good point. I missed that the build was --packages-above-and-dependencies, so that's good for me. Sorry for the noise.