RobotTrajectory as standard container

[DLu]

Description

Ported version of moveit/moveit#1162 for MoveIt2. This currently does not have any tests.

• Add iterator to RobotTrajectory class.
• Add .size() method to RobotTrajectory class.
• Add basic tests for RobotTrajectory class.
• Add equality operator for RobotState class in order to complete RobotTrajectory tests. Note: This seems outside the scope.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Merging #720 (f3d7964) into main (812a805) will increase coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head f3d7964 differs from pull request most recent head 9ebeac1. Consider uploading reports for the commit 9ebeac1 to get more accurate results

@@            Coverage Diff             @@
##             main     #720      +/-   ##
==========================================
+ Coverage   54.88%   54.92%   +0.05%     
==========================================
  Files         196      196              
  Lines       21359    21380      +21     
==========================================
+ Hits        11720    11741      +21     
  Misses       9639     9639              

Impacted Files	Coverage Δ
...include/moveit/robot_trajectory/robot_trajectory.h	90.77% <100.00%> (+4.73%)	⬆️
moveit_ros/moveit_servo/src/servo_node.cpp	68.89% <0.00%> (-0.67%)	⬇️

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[henningkayser]

Looks good. CI failure seems unrelated to me