[Issue-879] Add const specifier to moveit_core

[GayarUsmanov]

Description

This PR adds const specifiers to methods of some classes in moveit_core subdir as proposed in #879.

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-commenter]

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Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 45.64%. Comparing base (75286c7) to head (f17c57a).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...lude/moveit/robot_state/cartesian_interpolator.hpp	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3202      +/-   ##
==========================================
- Coverage   46.01%   45.64%   -0.37%     
==========================================
  Files         714      714              
  Lines       62304    62282      -22     
  Branches     7532     7529       -3     
==========================================
- Hits        28666    28421     -245     
- Misses      33471    33694     +223     
  Partials      167      167              

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[sea-bass]

Just one formatting failure, but otherwise looks good

[GayarUsmanov]

Just one formatting failure, but otherwise looks good

Thanks for pointing it out. Fixed.

[sjahr]

Thanks!