Refactor JTC command interface assignment

[dlanov]

Summary

Refactor the JointTrajectoryController command-interface assignment logic to make the selected command sources explicit and reduce nested conditionals.

Changes

• Rename tmp_command_ to closed_loop_pid_command_ to clarify that it stores preallocated closed-loop PID command output.
• Select velocity and effort command sources through named constant references.
• Preserve the existing position, velocity, acceleration, effort, and closed-loop PID command behavior.
• Add no allocations or additional work to the real-time update path.

Testing

• colcon build --symlink-install --packages-select joint_trajectory_controller --cmake-args -DBUILD_TESTING=ON
• colcon test --packages-select joint_trajectory_controller --event-handlers console_cohesion+
• colcon test-result --verbose
• pre-commit run --files joint_trajectory_controller/include/joint_trajectory_controller/joint_trajectory_controller.hpp joint_trajectory_controller/src/joint_trajectory_controller.cpp
• git diff --check

Results:

• 850 tests
• 0 errors
• 0 failures
• 0 skipped
• All applicable pre-commit checks passed

Closes #326

AI assistance

Claude Code assisted with analyzing and preparing the narrowly scoped refactor. I manually reviewed the complete diff and verified the build, test, formatting, lint, and whitespace-check results.

[destogl]

Looking good thanks!

[christophfroehlich]

the scope can be reduced inside the if-branches below, right? The ternary-if could even be used in assign_interface_from_point instead of assigning a new variable.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.83%. Comparing base (c7b97ca) to head (6a3c2d9).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2489   +/-   ##
=======================================
  Coverage   86.83%   86.83%           
=======================================
  Files         148      148           
  Lines       16273    16273           
  Branches     1368     1366    -2     
=======================================
  Hits        14131    14131           
  Misses       1635     1635           
  Partials      507      507           

Flag	Coverage Δ
unittests	86.83% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...jectory_controller/joint_trajectory_controller.hpp	62.50% <ø> (ø)
...ory_controller/src/joint_trajectory_controller.cpp	85.23% <100.00%> (ø)

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