[WAVE 1] Test cost printing across uneven multiphase states

[mickaelbegon]

Summary

• exercise Solution.print_cost() on a multiphase OCP whose phases have different state dimensions
• assert both phase-specific objective and constraint sections are evaluated
• preserve the current phase-local SolutionData behavior against the regression reported in Error sol.print_cost() #712

The faulty key-based concatenation described in #712 has already disappeared in the current implementation. This focused regression test documents and protects the corrected behavior.

Validation

• pytest tests/shard5/test_global_torque_driven_ocp.py::test_phase_transition_uneven_variable_number_by_mapping -q
• 2 passed

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This change is 

[mickaelbegon]

Wave 1 preparation update: this PR remains intentionally isolated. Full CI is waiting behind the shared Matplotlib prerequisite #1081; it will be marked ready after that lands and checks are rerun.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.26%. Comparing base (5ed90c1) to head (31527d0).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1076   +/-   ##
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  Coverage   77.26%   77.26%           
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  Files         196      196           
  Lines       21506    21506           
=======================================
  Hits        16616    16616           
  Misses       4890     4890           

Flag	Coverage Δ
unittests	77.26% <ø> (ø)

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