add knots to attrs

[kianorr]

Resolves #1136

Adds knots to attrs in _check_type such that there is an error if the knots are different between different coils. This way, the user has to use a MixedCoilSet

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.24%. Comparing base (b15a24f) to head (e6840de).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1142      +/-   ##
==========================================
- Coverage   95.24%   95.24%   -0.01%     
==========================================
  Files          87       87              
  Lines       21947    21947              
==========================================
- Hits        20904    20903       -1     
- Misses       1043     1044       +1     

Files	Coverage Δ
desc/coils.py	97.10% <ø> (ø)

... and 1 file with indirect coverage changes

[f0uriest]

Remember to do the same for breakpoints in #970

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     -2.64 +/- 8.42     | -1.44e-02 +/- 4.59e-02 |  5.30e-01 +/- 4.1e-02  |  5.45e-01 +/- 2.0e-02  |
 test_build_transform_fft_midres         |     -0.24 +/- 3.68     | -1.48e-03 +/- 2.26e-02 |  6.12e-01 +/- 9.3e-03  |  6.14e-01 +/- 2.1e-02  |
 test_build_transform_fft_highres        |     -0.91 +/- 3.65     | -9.18e-03 +/- 3.70e-02 |  1.00e+00 +/- 3.2e-02  |  1.01e+00 +/- 1.8e-02  |
 test_equilibrium_init_lowres            |     -7.07 +/- 5.79     | -2.85e-01 +/- 2.34e-01 |  3.75e+00 +/- 1.7e-01  |  4.03e+00 +/- 1.6e-01  |
 test_equilibrium_init_medres            |     -4.89 +/- 3.71     | -2.14e-01 +/- 1.62e-01 |  4.16e+00 +/- 1.0e-01  |  4.37e+00 +/- 1.3e-01  |
 test_equilibrium_init_highres           |     -2.08 +/- 2.52     | -1.19e-01 +/- 1.44e-01 |  5.61e+00 +/- 1.2e-01  |  5.72e+00 +/- 8.0e-02  |
 test_objective_compile_dshape_current   |     -2.32 +/- 1.98     | -9.17e-02 +/- 7.84e-02 |  3.87e+00 +/- 6.4e-02  |  3.96e+00 +/- 4.6e-02  |
 test_objective_compile_atf              |     -2.82 +/- 2.03     | -2.40e-01 +/- 1.72e-01 |  8.26e+00 +/- 1.2e-01  |  8.50e+00 +/- 1.2e-01  |
 test_objective_compute_dshape_current   |     -2.93 +/- 3.36     | -3.76e-05 +/- 4.31e-05 |  1.24e-03 +/- 2.5e-05  |  1.28e-03 +/- 3.5e-05  |
 test_objective_compute_atf              |     -0.28 +/- 5.41     | -1.21e-05 +/- 2.30e-04 |  4.25e-03 +/- 1.6e-04  |  4.26e-03 +/- 1.6e-04  |
 test_objective_jac_dshape_current       |     -2.06 +/- 8.93     | -7.58e-04 +/- 3.29e-03 |  3.60e-02 +/- 2.2e-03  |  3.68e-02 +/- 2.4e-03  |
 test_objective_jac_atf                  |     -3.11 +/- 3.60     | -5.90e-02 +/- 6.83e-02 |  1.84e+00 +/- 4.2e-02  |  1.90e+00 +/- 5.4e-02  |
 test_perturb_1                          |     -4.40 +/- 1.71     | -6.26e-01 +/- 2.43e-01 |  1.36e+01 +/- 1.9e-01  |  1.42e+01 +/- 1.6e-01  |
 test_perturb_2                          |     -2.05 +/- 2.86     | -3.90e-01 +/- 5.44e-01 |  1.86e+01 +/- 3.2e-01  |  1.90e+01 +/- 4.4e-01  |
 test_proximal_jac_atf                   |     +0.65 +/- 0.74     | +4.76e-02 +/- 5.45e-02 |  7.42e+00 +/- 3.1e-02  |  7.37e+00 +/- 4.5e-02  |
 test_proximal_freeb_compute             |     -1.59 +/- 0.86     | -2.86e-03 +/- 1.54e-03 |  1.77e-01 +/- 1.1e-03  |  1.80e-01 +/- 1.1e-03  |
 test_proximal_freeb_jac                 |     -1.10 +/- 2.05     | -8.19e-02 +/- 1.53e-01 |  7.39e+00 +/- 1.1e-01  |  7.47e+00 +/- 1.1e-01  |
 test_solve_fixed_iter                   |     +0.67 +/- 7.73     | +1.21e-01 +/- 1.39e+00 |  1.81e+01 +/- 1.2e+00  |  1.80e+01 +/- 7.8e-01  |