Calculate frame difference

[francesco-donofrio]

This PR introduces a method to compute frame differences, along with a corresponding KDL implementation.

[aprotyas]

Why not imbibe the size constraints?

Suggested change

	std::vector<double> & x_a_vec, std::vector<double> & x_b_vec, double dt,
	std::vector<double> & delta_x_vec);
	std::array<double, 7> & x_a_vec, std::array<double, 7> & x_b_vec, double dt,
	std::array<double, 6> & delta_x_vec);

[francesco-donofrio]

I used std::vector<double> to maintain consistency with the convert_joint_deltas_to_cartesian_deltas method, where std::vector<double> is used for the delta_x parameter.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 10 lines in your changes missing coverage. Please review.

Project coverage is 80.00%. Comparing base (4d6bada) to head (210a57f).

Files with missing lines	Patch %	Lines
kinematics_interface/src/kinematics_interface.cpp	47.05%	6 Missing and 3 partials ⚠️
...ics_interface_kdl/src/kinematics_interface_kdl.cpp	94.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
- Coverage   80.20%   80.00%   -0.21%     
==========================================
  Files           4        4              
  Lines         197      245      +48     
  Branches       35       52      +17     
==========================================
+ Hits          158      196      +38     
- Misses         28       34       +6     
- Partials       11       15       +4     

Flag	Coverage Δ
unittests	80.00% <80.00%> (-0.21%)	⬇️

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

Files with missing lines	Coverage Δ
...lude/kinematics_interface/kinematics_interface.hpp	100.00% <ø> (ø)
...terface_kdl/test/test_kinematics_interface_kdl.cpp	100.00% <100.00%> (ø)
...ics_interface_kdl/src/kinematics_interface_kdl.cpp	70.43% <94.11%> (+3.43%)	⬆️
kinematics_interface/src/kinematics_interface.cpp	65.90% <47.05%> (-11.87%)	⬇️