stomp: Fix passing different types to std::min in cost_functions.hpp

[traversaro]

Description

std::min supports comparing scalar of the same type. Depending on the specific platform or compiler, values.cols() return type may not be compatible with long, so explicitly casting ensure that std::min compiles fine on any platform.

Specifically, I had encountered a compilation problem with this when compiling moveit with MSVC 2019.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 45.64%. Comparing base (b5eb4de) to head (9eef663).
Report is 1 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3244      +/-   ##
==========================================
- Coverage   45.66%   45.64%   -0.02%     
==========================================
  Files         714      714              
  Lines       62296    62298       +2     
  Branches     7531     7529       -2     
==========================================
- Hits        28442    28427      -15     
- Misses      33688    33705      +17     
  Partials      166      166              

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