Fix constraint2() call and spelling errors from code review

[Copilot]

Addresses review comments from copilot-pull-request-reviewer bot on PR #403.

Changes

• Logic fix: ConstrainedOptProblem.cpp:80 now calls constraint2() instead of constraint1() twice when processing TwinDoubleExpressionInequality

  // Before: incorrectly called constraint1() for both constraints
  DoubleExpressionInequality::shared_ptr p2 = p->constraint1();
  
  // After: correctly retrieves second constraint
  DoubleExpressionInequality::shared_ptr p2 = p->constraint2();

• Spelling corrections in comments/docs across 6 files:

  • probelm → problem
  • cosntraints/cosntraint → constraints/constraint
  • constriant → constraint
  • expaned_mat → expanded_mat (variable name)

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