Update rules for chunking jacobian

[f0uriest]

Resolves #1276

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     -6.71 +/- 9.21     | -3.89e-02 +/- 5.33e-02 |  5.40e-01 +/- 5.0e-02  |  5.79e-01 +/- 2.0e-02  |
 test_equilibrium_init_medres            |     -5.99 +/- 6.32     | -2.72e-01 +/- 2.87e-01 |  4.27e+00 +/- 2.5e-01  |  4.54e+00 +/- 1.4e-01  |
 test_equilibrium_init_highres           |     +2.35 +/- 6.90     | +1.33e-01 +/- 3.88e-01 |  5.76e+00 +/- 3.5e-01  |  5.63e+00 +/- 1.8e-01  |
 test_objective_compile_dshape_current   |     +0.25 +/- 3.23     | +9.99e-03 +/- 1.28e-01 |  3.95e+00 +/- 1.1e-01  |  3.94e+00 +/- 7.2e-02  |
 test_objective_compute_dshape_current   |     -6.47 +/- 5.27     | -2.53e-04 +/- 2.06e-04 |  3.66e-03 +/- 7.4e-05  |  3.91e-03 +/- 1.9e-04  |
 test_objective_jac_dshape_current       |     +0.17 +/- 5.77     | +7.48e-05 +/- 2.47e-03 |  4.29e-02 +/- 2.0e-03  |  4.28e-02 +/- 1.4e-03  |
 test_perturb_2                          |     -2.39 +/- 8.42     | -4.56e-01 +/- 1.61e+00 |  1.86e+01 +/- 1.6e+00  |  1.91e+01 +/- 2.9e-01  |
 test_proximal_freeb_jac                 |     -0.80 +/- 2.60     | -6.18e-02 +/- 2.00e-01 |  7.63e+00 +/- 9.5e-02  |  7.70e+00 +/- 1.8e-01  |
 test_solve_fixed_iter                   |     -0.31 +/- 59.29    | -1.59e-02 +/- 3.08e+00 |  5.17e+00 +/- 2.2e+00  |  5.19e+00 +/- 2.2e+00  |
 test_build_transform_fft_midres         |     -0.18 +/- 2.24     | -1.09e-03 +/- 1.38e-02 |  6.15e-01 +/- 8.9e-03  |  6.16e-01 +/- 1.1e-02  |
 test_build_transform_fft_highres        |     +0.67 +/- 3.24     | +6.78e-03 +/- 3.28e-02 |  1.02e+00 +/- 3.2e-02  |  1.01e+00 +/- 8.1e-03  |
 test_equilibrium_init_lowres            |     +0.52 +/- 2.34     | +1.99e-02 +/- 9.01e-02 |  3.87e+00 +/- 8.7e-02  |  3.85e+00 +/- 2.2e-02  |
 test_objective_compile_atf              |     +1.52 +/- 3.80     | +1.19e-01 +/- 2.99e-01 |  7.97e+00 +/- 1.9e-01  |  7.85e+00 +/- 2.3e-01  |
 test_objective_compute_atf              |     -0.28 +/- 3.26     | -2.99e-05 +/- 3.46e-04 |  1.06e-02 +/- 2.0e-04  |  1.06e-02 +/- 2.8e-04  |
 test_objective_jac_atf                  |     -0.62 +/- 3.01     | -1.21e-02 +/- 5.86e-02 |  1.94e+00 +/- 3.9e-02  |  1.95e+00 +/- 4.4e-02  |
 test_perturb_1                          |     +0.94 +/- 2.00     | +1.19e-01 +/- 2.53e-01 |  1.28e+01 +/- 1.6e-01  |  1.27e+01 +/- 2.0e-01  |
 test_proximal_jac_atf                   |     +0.08 +/- 0.66     | +6.64e-03 +/- 5.37e-02 |  8.17e+00 +/- 3.8e-02  |  8.16e+00 +/- 3.8e-02  |
 test_proximal_freeb_compute             |     -0.51 +/- 1.29     | -9.46e-04 +/- 2.37e-03 |  1.83e-01 +/- 1.2e-03  |  1.84e-01 +/- 2.0e-03  |

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.47%. Comparing base (f0bf028) to head (5ab0a7c).
Report is 1874 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1283   +/-   ##
=======================================
  Coverage   95.47%   95.47%           
=======================================
  Files          96       96           
  Lines       23896    23899    +3     
=======================================
+ Hits        22814    22817    +3     
  Misses       1082     1082           

Files with missing lines	Coverage Δ
desc/objectives/getters.py	95.12% <100.00%> (+0.06%)	⬆️
desc/objectives/objective_funs.py	94.75% <100.00%> (+0.01%)	⬆️

[dpanici]

Should put a note in the docstring of _Objective of what "auto" for jac_chunk_size does now (uses a conservative heuristic estimate based on problem size)

[f0uriest]

Should put a note in the docstring of _Objective of what "auto" for jac_chunk_size does now (uses a conservative heuristic estimate based on problem size)

"auto" is still only an option for ObjectiveFunction, not _Objective so I don't think it makes sense to describe it there.

[YigitElma]

This is again a design choice but let's say I have a single objective,

objective = ObjectiveFunction(ForceBalance(eq, jac_chunk_size))

This may complicate the logic but could we add something like errorif( ..... and not len(self._objectives) == 1) ?

Some other edge case could be giving same jac_chunk_size to each objective, which should be allowed but I don't think anyone wanna use it that way, it is more laborious...