Add puddle objective to avoid local min in current potential

[dpanici]

TODO: decide on better metric, look at Fu 2024

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     +2.49 +/- 5.93     | +1.44e-02 +/- 3.44e-02 |  5.94e-01 +/- 2.6e-02  |  5.79e-01 +/- 2.2e-02  |
 test_equilibrium_init_medres            |     +1.29 +/- 2.13     | +5.97e-02 +/- 9.91e-02 |  4.71e+00 +/- 7.4e-02  |  4.65e+00 +/- 6.6e-02  |
 test_equilibrium_init_highres           |     +0.67 +/- 1.69     | +3.96e-02 +/- 1.00e-01 |  5.97e+00 +/- 8.7e-02  |  5.93e+00 +/- 5.0e-02  |
 test_objective_compile_dshape_current   |     +1.10 +/- 1.91     | +4.54e-02 +/- 7.89e-02 |  4.18e+00 +/- 6.5e-02  |  4.14e+00 +/- 4.4e-02  |
 test_objective_compute_dshape_current   |     +3.62 +/- 6.32     | +1.98e-04 +/- 3.46e-04 |  5.67e-03 +/- 2.2e-04  |  5.47e-03 +/- 2.7e-04  |
 test_objective_jac_dshape_current       |     -2.86 +/- 10.09    | -1.32e-03 +/- 4.68e-03 |  4.50e-02 +/- 2.8e-03  |  4.63e-02 +/- 3.7e-03  |
 test_perturb_2                          |     +0.16 +/- 2.46     | +3.35e-02 +/- 5.30e-01 |  2.15e+01 +/- 3.4e-01  |  2.15e+01 +/- 4.1e-01  |
 test_proximal_freeb_jac                 |     -0.66 +/- 1.77     | -5.03e-02 +/- 1.35e-01 |  7.61e+00 +/- 1.1e-01  |  7.66e+00 +/- 8.4e-02  |
 test_solve_fixed_iter                   |     +0.61 +/- 2.25     | +2.10e-01 +/- 7.70e-01 |  3.45e+01 +/- 6.5e-01  |  3.43e+01 +/- 4.1e-01  |
 test_LinearConstraintProjection_build   |     -0.53 +/- 3.32     | -5.94e-02 +/- 3.69e-01 |  1.10e+01 +/- 3.0e-01  |  1.11e+01 +/- 2.2e-01  |
 test_build_transform_fft_midres         |     -0.89 +/- 2.74     | -5.88e-03 +/- 1.81e-02 |  6.55e-01 +/- 9.7e-03  |  6.61e-01 +/- 1.5e-02  |
 test_build_transform_fft_highres        |     -0.86 +/- 2.39     | -8.74e-03 +/- 2.43e-02 |  1.01e+00 +/- 2.1e-02  |  1.02e+00 +/- 1.2e-02  |
 test_equilibrium_init_lowres            |     -1.84 +/- 3.34     | -7.92e-02 +/- 1.43e-01 |  4.22e+00 +/- 1.1e-01  |  4.30e+00 +/- 9.2e-02  |
 test_objective_compile_atf              |     -0.60 +/- 2.95     | -4.95e-02 +/- 2.45e-01 |  8.25e+00 +/- 1.5e-01  |  8.30e+00 +/- 1.9e-01  |
 test_objective_compute_atf              |     +3.30 +/- 4.57     | +5.26e-04 +/- 7.27e-04 |  1.64e-02 +/- 6.9e-04  |  1.59e-02 +/- 2.2e-04  |
 test_objective_jac_atf                  |     +0.76 +/- 2.59     | +1.51e-02 +/- 5.15e-02 |  2.00e+00 +/- 3.5e-02  |  1.99e+00 +/- 3.7e-02  |
 test_perturb_1                          |     +3.60 +/- 3.47     | +5.48e-01 +/- 5.27e-01 |  1.58e+01 +/- 2.7e-01  |  1.52e+01 +/- 4.6e-01  |
 test_proximal_jac_atf                   |     +0.65 +/- 1.37     | +5.39e-02 +/- 1.14e-01 |  8.36e+00 +/- 8.5e-02  |  8.31e+00 +/- 7.5e-02  |
 test_proximal_freeb_compute             |     +0.22 +/- 1.46     | +4.50e-04 +/- 2.95e-03 |  2.02e-01 +/- 1.7e-03  |  2.02e-01 +/- 2.4e-03  |
 test_solve_fixed_iter_compiled          |     +1.05 +/- 1.69     | +2.21e-01 +/- 3.57e-01 |  2.13e+01 +/- 2.2e-01  |  2.11e+01 +/- 2.8e-01  |