fix(ik): trajectory residual is the maximum, and document trajectory behaviour

[petercorke]

Summary

• For a trajectory of poses, IKSolver.solve (so all ikine_* methods) returned the minimum residual over the poses, which hid poses solved badly or not at all. It is now the maximum, the worst case.
• Trajectory behaviour was undocumented. It is now described in IKSolver.solve, the ikine_LM/NR/GN/QP methods of ETS and RobotKinematics, DHRobot.ikine_LM and docs/source/IK/ik.rst: accepted inputs (SE3 with N poses or an (N, 4, 4) array), q of shape (N, n), every pose seeded with the same q0 (so consecutive solutions may be on different IK branches), and how success, iterations, searches, residual and reason are combined. A versionchanged:: 1.4.5 notice records the residual change.
• Docs that were wrong are corrected:
  • ik_NR / ik_GN (in ETS and RobotKinematics) said they accept a pose trajectory. The C++ solvers take a single 4x4 pose and raise TypeError otherwise.
  • ETS.ik_GN and ik.rst said the C++ solvers return a tuple. They return an IKSolution.

Behaviour change

Only the trajectory residual value changes (min to max). Single-pose results are unchanged. Code that checks sol.success is unaffected. Code that relied on the old minimum as a "best pose" measure would see a larger value.

Test plan

• tests/test_IK.py and tests/test_ik_joint_limits.py pass locally
• New test_trajectory_residual_is_maximum (stub solver, known residuals) and test_trajectory_failure_is_reported (one reachable, one unreachable pose) both fail on main and pass here
• CI

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
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🟢 Metrics 5 complexity · 0 duplication

Metric	Results
Complexity	5
Duplication	0

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (acc6842) to head (d2fb0d1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/roboticstoolbox/robot/IK.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #712   +/-   ##
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  Coverage   0.00%   0.00%           
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  Files        143     143           
  Lines      14269   14269           
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  Misses     14269   14269           

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