Simplified Bout computation in free boundary

[unalmis]

This PR goal is to separate the computation of the inner and outer magnetic fields in the free boundary problem. The plan is to do constrained optimization to avoid inverting the large system for the Fourier harmonics of ϕ.

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|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_midres         |     -1.30 +/- 8.12     | -8.60e-03 +/- 5.38e-02 |  6.54e-01 +/- 4.7e-02  |  6.62e-01 +/- 2.7e-02  |
 test_build_transform_fft_highres        |     +0.02 +/- 4.25     | +2.32e-04 +/- 3.98e-02 |  9.35e-01 +/- 3.9e-02  |  9.35e-01 +/- 9.8e-03  |
 test_equilibrium_init_lowres            |     +0.69 +/- 1.64     | +2.82e-02 +/- 6.67e-02 |  4.11e+00 +/- 4.2e-02  |  4.08e+00 +/- 5.2e-02  |
 test_objective_compile_atf              |     -0.41 +/- 2.20     | -3.44e-02 +/- 1.85e-01 |  8.40e+00 +/- 1.5e-01  |  8.43e+00 +/- 1.0e-01  |
 test_objective_compute_atf              |     -0.22 +/- 2.06     | -3.55e-05 +/- 3.36e-04 |  1.63e-02 +/- 2.5e-04  |  1.63e-02 +/- 2.3e-04  |
 test_objective_jac_atf                  |     +0.73 +/- 1.92     | +1.45e-02 +/- 3.80e-02 |  1.99e+00 +/- 3.0e-02  |  1.97e+00 +/- 2.3e-02  |
 test_perturb_1                          |     +0.15 +/- 2.53     | +2.34e-02 +/- 3.90e-01 |  1.54e+01 +/- 3.8e-01  |  1.54e+01 +/- 9.6e-02  |
 test_proximal_jac_atf                   |     +0.75 +/- 1.22     | +6.03e-02 +/- 9.89e-02 |  8.16e+00 +/- 7.6e-02  |  8.10e+00 +/- 6.3e-02  |
+test_proximal_freeb_compute             |    -10.01 +/- 1.26     | -2.17e-02 +/- 2.73e-03 |  1.95e-01 +/- 2.3e-03  |  2.17e-01 +/- 1.4e-03  |
 test_solve_fixed_iter                   |     -0.21 +/- 1.66     | -6.86e-02 +/- 5.54e-01 |  3.32e+01 +/- 2.9e-01  |  3.33e+01 +/- 4.7e-01  |
 test_objective_compute_ripple           |     +0.59 +/- 2.33     | +4.10e-03 +/- 1.62e-02 |  7.00e-01 +/- 1.4e-02  |  6.96e-01 +/- 8.7e-03  |
 test_objective_grad_ripple              |     +0.19 +/- 1.64     | +5.05e-03 +/- 4.36e-02 |  2.66e+00 +/- 3.3e-02  |  2.66e+00 +/- 2.8e-02  |
 test_build_transform_fft_lowres         |     +0.48 +/- 2.42     | +3.20e-03 +/- 1.60e-02 |  6.65e-01 +/- 1.0e-02  |  6.62e-01 +/- 1.2e-02  |
 test_equilibrium_init_medres            |     -0.95 +/- 0.91     | -4.46e-02 +/- 4.29e-02 |  4.67e+00 +/- 3.7e-02  |  4.71e+00 +/- 2.2e-02  |
 test_equilibrium_init_highres           |     +0.33 +/- 4.03     | +1.88e-02 +/- 2.30e-01 |  5.72e+00 +/- 2.2e-01  |  5.70e+00 +/- 6.1e-02  |
 test_objective_compile_dshape_current   |     -3.18 +/- 6.64     | -1.41e-01 +/- 2.96e-01 |  4.31e+00 +/- 2.6e-01  |  4.45e+00 +/- 1.4e-01  |
 test_objective_compute_dshape_current   |     +0.78 +/- 3.87     | +4.46e-05 +/- 2.20e-04 |  5.75e-03 +/- 1.7e-04  |  5.70e-03 +/- 1.4e-04  |
 test_objective_jac_dshape_current       |     +1.63 +/- 6.44     | +7.19e-04 +/- 2.84e-03 |  4.49e-02 +/- 1.9e-03  |  4.41e-02 +/- 2.1e-03  |
 test_perturb_2                          |     -0.94 +/- 1.86     | -2.08e-01 +/- 4.10e-01 |  2.18e+01 +/- 2.5e-01  |  2.20e+01 +/- 3.2e-01  |
 test_proximal_jac_atf_with_eq_update    |     -0.56 +/- 0.85     | -9.64e-02 +/- 1.46e-01 |  1.71e+01 +/- 1.2e-01  |  1.72e+01 +/- 8.6e-02  |
+test_proximal_freeb_jac                 |    -32.01 +/- 2.35     | -2.46e+00 +/- 1.81e-01 |  5.23e+00 +/- 1.3e-01  |  7.70e+00 +/- 1.3e-01  |
 test_solve_fixed_iter_compiled          |     +0.14 +/- 0.82     | +3.13e-02 +/- 1.77e-01 |  2.17e+01 +/- 1.6e-01  |  2.16e+01 +/- 6.7e-02  |
 test_LinearConstraintProjection_build   |     -0.16 +/- 2.35     | -1.93e-02 +/- 2.81e-01 |  1.19e+01 +/- 1.8e-01  |  1.19e+01 +/- 2.1e-01  |
 test_objective_compute_ripple_spline    |     +1.14 +/- 1.64     | +4.02e-03 +/- 5.77e-03 |  3.57e-01 +/- 4.0e-03  |  3.53e-01 +/- 4.2e-03  |
 test_objective_grad_ripple_spline       |     -0.01 +/- 2.16     | -1.65e-04 +/- 3.07e-02 |  1.42e+00 +/- 2.3e-02  |  1.42e+00 +/- 2.0e-02  |