Foundation Classes - Modernize Bnd_B2 and Bnd_B3 (#838)

Foundation Classes - Modernize Bnd_B2 and Bnd_B3 (#838)

  - Replace C-style arrays with std::array for internal storage (myCenter and myHSize fields)
  - Add constexpr noexcept constructors for all variants (default, gp_XY/gp_XYZ, and std::array overloads)
  - Add public getter methods Center() and HSize() for direct read access to internal fields
  - Add setter overloads accepting std::array parameters
  - Mark appropriate methods as constexpr and noexcept for compile-time evaluation and optimization guarantees
  - Clean up boolean comparisons (remove explicit Standard_True/False checks)