added: pretty-print box constraints

[franckgaga]

Before:

LinMPC controller with a sample time Ts = 4.0 s:
├ estimator: SteadyKalmanFilter
├ model: LinModel
├ optimizer: OSQP 
├ transcription: MultipleShooting
└ dimensions:
  │ ├ 10 prediction steps Hp
  │ ├  5 control steps Hc
  │ ├  2 manipulated inputs u (0 integrating states)
  │ ├  6 estimated states x̂
  │ ├  2 measured outputs ym (2 integrating states)
  │ ├  0 unmeasured outputs yu
  │ └  1 measured disturbances d
  └ optimization:
    ├ 71 decision variables Z̃ (1 slack variable)
    ├ 40 linear inequality constraints A (0 custom)
    └ 60 linear equality constraints Aeq

After:

LinMPC controller with a sample time Ts = 4.0 s:
├ estimator: SteadyKalmanFilter
├ model: LinModel
├ optimizer: OSQP 
├ transcription: MultipleShooting
└ dimensions:
  │ ├ 10 prediction steps Hp
  │ ├  5 control steps Hc
  │ ├  2 manipulated inputs u (0 integrating states)
  │ ├  6 estimated states x̂
  │ ├  2 measured outputs ym (2 integrating states)
  │ ├  0 unmeasured outputs yu
  │ └  1 measured disturbances d
  └ optimization:
    ├ 71 decision variables Z̃ (1 slack variable, 21 bounds) # <--- new info
    ├ 40 linear inequality constraints A (0 custom)
    └ 60 linear equality constraints Aeq