Add qfm surface functionality

[dpanici]

Resolve #1162

• add tutorial for this
• allow ToroidalFlux to accept FourierRZToroidalSurface so that we can specify the toroidal flux through the QFM (we can do the vector potential method on the surface just fine so this should be easy, and there is no plasma current to consider either)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.44%. Comparing base (1e4147d) to head (4268ec2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1264      +/-   ##
==========================================
- Coverage   95.44%   95.44%   -0.01%     
==========================================
  Files          95       95              
  Lines       23423    23437      +14     
==========================================
+ Hits        22357    22369      +12     
- Misses       1066     1068       +2     

Files with missing lines	Coverage Δ
desc/objectives/_coils.py	99.20% <100.00%> (+0.03%)	⬆️

... and 2 files with indirect coverage changes

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_midres         |     -9.93 +/- 4.36     | -6.57e-02 +/- 2.88e-02 |  5.96e-01 +/- 2.7e-02  |  6.62e-01 +/- 1.1e-02  |
 test_build_transform_fft_highres        |     -3.26 +/- 4.25     | -3.42e-02 +/- 4.45e-02 |  1.01e+00 +/- 3.7e-02  |  1.05e+00 +/- 2.5e-02  |
 test_equilibrium_init_lowres            |     +4.35 +/- 6.40     | +1.64e-01 +/- 2.41e-01 |  3.94e+00 +/- 1.7e-01  |  3.77e+00 +/- 1.7e-01  |
 test_objective_compile_atf              |     -1.05 +/- 4.01     | -8.10e-02 +/- 3.11e-01 |  7.66e+00 +/- 2.4e-01  |  7.74e+00 +/- 2.0e-01  |
 test_objective_compute_atf              |     -0.24 +/- 2.41     | -2.53e-05 +/- 2.55e-04 |  1.05e-02 +/- 1.5e-04  |  1.06e-02 +/- 2.0e-04  |
 test_objective_jac_atf                  |     +3.98 +/- 3.39     | +7.39e-02 +/- 6.30e-02 |  1.93e+00 +/- 4.2e-02  |  1.86e+00 +/- 4.7e-02  |
 test_perturb_1                          |     +4.93 +/- 2.98     | +6.06e-01 +/- 3.67e-01 |  1.29e+01 +/- 3.0e-01  |  1.23e+01 +/- 2.2e-01  |
 test_proximal_jac_atf                   |     +1.62 +/- 1.12     | +1.31e-01 +/- 9.08e-02 |  8.23e+00 +/- 7.2e-02  |  8.10e+00 +/- 5.5e-02  |
-test_proximal_freeb_compute             |     +3.79 +/- 1.09     | +6.90e-03 +/- 1.97e-03 |  1.89e-01 +/- 1.1e-03  |  1.82e-01 +/- 1.6e-03  |
 test_build_transform_fft_lowres         |     +0.26 +/- 6.85     | +1.43e-03 +/- 3.78e-02 |  5.53e-01 +/- 2.9e-02  |  5.52e-01 +/- 2.4e-02  |
 test_equilibrium_init_medres            |     +0.44 +/- 2.72     | +1.92e-02 +/- 1.17e-01 |  4.33e+00 +/- 8.2e-02  |  4.31e+00 +/- 8.4e-02  |
 test_equilibrium_init_highres           |     +0.20 +/- 1.49     | +1.10e-02 +/- 8.42e-02 |  5.66e+00 +/- 6.2e-02  |  5.65e+00 +/- 5.6e-02  |
 test_objective_compile_dshape_current   |     +0.39 +/- 1.22     | +1.53e-02 +/- 4.80e-02 |  3.93e+00 +/- 4.0e-02  |  3.92e+00 +/- 2.6e-02  |
 test_objective_compute_dshape_current   |     +0.29 +/- 2.08     | +1.05e-05 +/- 7.53e-05 |  3.63e-03 +/- 5.5e-05  |  3.62e-03 +/- 5.1e-05  |
 test_objective_jac_dshape_current       |     +2.13 +/- 6.81     | +8.69e-04 +/- 2.77e-03 |  4.16e-02 +/- 1.4e-03  |  4.07e-02 +/- 2.4e-03  |
 test_perturb_2                          |     -0.30 +/- 1.39     | -5.38e-02 +/- 2.53e-01 |  1.82e+01 +/- 1.9e-01  |  1.82e+01 +/- 1.7e-01  |
 test_proximal_freeb_jac                 |     +1.18 +/- 1.89     | +8.89e-02 +/- 1.42e-01 |  7.62e+00 +/- 1.2e-01  |  7.53e+00 +/- 7.9e-02  |
 test_solve_fixed_iter                   |     -1.44 +/- 59.07    | -7.41e-02 +/- 3.03e+00 |  5.06e+00 +/- 2.1e+00  |  5.13e+00 +/- 2.2e+00  |

[f0uriest]

should maybe add a note to use BoundaryError or VacuumBoundaryError for free boundary / single stage optimization

[f0uriest]

would prefer an actual instance check here instead of relying on attributes to be/not be there

[dpanici]

make a new objective for this specifically

[dpanici]

update if #1205 is merged first