feat: Added new statistics interface / removed statistics publisher

[jmachowinski]

Description

This removes the half backed statistics implementation and replaces it with a interface that can be implemented by a third party pkg to archive the same functionality.

Is this user-facing behavior change?

Yes, we remove an existing feature. Due to recent bug reports I believe almost nobody was using it.
But as states, this also enables community pkgs to replicate the existing behavior.

Did you use Generative AI?

Yes, SWE-1.7

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[jmachowinski]

Pulls: #3203
Gist: https://gist.githubusercontent.com/jmachowinski/43427d9eb5ad9b3e5aff3061c21666bc/raw/e02b86c54cc2197263e6a285fba45a2077543125/ros2.repos
BUILD args:
TEST args:
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/19897

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[jmachowinski]

This reduced the compile time of a node with 1 sub and 1 publisher from 6.32s to 4.91s on a Ryzen 9900X

[fujitatomoya]

I am not against this approach, imo old implementation clearly wasn't pulling its weight anyway. a few comments below.

• should we not give deprecation period before removal? statistics has been there for a long time, there would be some users who might use the statistics.
• no default implementation provided by mainline? i think user can still do enable/disable the statistics feature on the subscription, and then mainline provides the default collector?
• this still supports rclcpp-only, so rclpy and other client libraries can't benefit. we know that this is the same limitation the old design had. probably this is next step after this PR, for longer term I think that statistics hooks is an rcl-level event/emission API, which would give all client libraries and all entity types (publishers, services, actions) a shared mechanism, with a default implementation maintained and tested in mainline.