Type safety for CartesianInterpolator

[wyattrees]

Description

Overloads of CartesianInterpolator::computeCartesianPath may return a distance or a percentage value, while the return type is always double. This PR introduces type safety for these return values.

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

[tylerjw]

This is a nice change. It is really helpful when your compiler can help you detect logic errors.

[codecov]

Codecov Report

Merging #1325 (97c5a1e) into main (99c73e6) will decrease coverage by 0.04%.
The diff coverage is 42.31%.

@@            Coverage Diff             @@
##             main    #1325      +/-   ##
==========================================
- Coverage   61.41%   61.38%   -0.03%     
==========================================
  Files         274      274              
  Lines       24963    24979      +16     
==========================================
+ Hits        15329    15331       +2     
- Misses       9634     9648      +14     

Impacted Files	Coverage Δ
...nclude/moveit/robot_state/cartesian_interpolator.h	57.90% <41.67%> (-27.81%)	⬇️
...it_core/robot_state/src/cartesian_interpolator.cpp	39.42% <42.86%> (-0.43%)	⬇️
...nning_scene_monitor/src/planning_scene_monitor.cpp	45.29% <0.00%> (-0.43%)	⬇️

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