Don't keep reference to data_index in alias partial objects

[f0uriest]

a functools.partial object that we use for aliases keeps a copy of all of its closed over args, which meant that each alias kept a full copy of the entire data index. I don't think it's the source of any major memory leak, but it is risky so this fixes it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.71%. Comparing base (072f66b) to head (5ac0365).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #942   +/-   ##
=======================================
  Coverage   94.71%   94.71%           
=======================================
  Files          86       86           
  Lines       21198    21198           
=======================================
  Hits        20078    20078           
  Misses       1120     1120           

Files	Coverage Δ
desc/compute/data_index.py	95.55% <100.00%> (ø)

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     +0.49 +/- 1.43     | +4.35e-05 +/- 1.28e-04 |  9.00e-03 +/- 8.0e-05  |  8.95e-03 +/- 9.9e-05  |
 test_build_transform_fft_midres         |     +0.94 +/- 1.03     | +8.14e-04 +/- 8.97e-04 |  8.75e-02 +/- 6.1e-04  |  8.67e-02 +/- 6.6e-04  |
 test_build_transform_fft_highres        |     +0.20 +/- 0.76     | +9.22e-04 +/- 3.44e-03 |  4.54e-01 +/- 2.2e-03  |  4.53e-01 +/- 2.7e-03  |
 test_equilibrium_init_lowres            |     +0.45 +/- 1.40     | +1.17e-03 +/- 3.61e-03 |  2.59e-01 +/- 2.1e-03  |  2.58e-01 +/- 3.0e-03  |
 test_equilibrium_init_medres            |     +0.76 +/- 1.15     | +4.50e-03 +/- 6.84e-03 |  5.97e-01 +/- 4.7e-03  |  5.93e-01 +/- 5.0e-03  |
 test_equilibrium_init_highres           |     -0.01 +/- 1.39     | -2.47e-04 +/- 2.99e-02 |  2.15e+00 +/- 1.5e-02  |  2.15e+00 +/- 2.6e-02  |
 test_objective_compile_dshape_current   |     -0.22 +/- 8.06     | -8.23e-03 +/- 3.07e-01 |  3.80e+00 +/- 2.2e-01  |  3.81e+00 +/- 2.1e-01  |
 test_objective_compile_atf              |     +0.00 +/- 4.69     | +3.55e-04 +/- 3.53e-01 |  7.52e+00 +/- 2.3e-01  |  7.52e+00 +/- 2.7e-01  |
 test_objective_compute_dshape_current   |     -1.92 +/- 2.01     | -1.02e-04 +/- 1.07e-04 |  5.20e-03 +/- 5.2e-05  |  5.30e-03 +/- 9.3e-05  |
 test_objective_compute_atf              |     +0.42 +/- 1.54     | +4.65e-05 +/- 1.70e-04 |  1.11e-02 +/- 1.5e-04  |  1.11e-02 +/- 7.8e-05  |
 test_objective_jac_dshape_current       |     +0.31 +/- 5.42     | +1.42e-04 +/- 2.47e-03 |  4.56e-02 +/- 2.1e-03  |  4.55e-02 +/- 1.3e-03  |
 test_objective_jac_atf                  |     +0.79 +/- 3.05     | +1.63e-02 +/- 6.30e-02 |  2.08e+00 +/- 4.5e-02  |  2.07e+00 +/- 4.4e-02  |
 test_perturb_1                          |     -0.83 +/- 3.07     | -1.26e-01 +/- 4.65e-01 |  1.50e+01 +/- 2.8e-01  |  1.52e+01 +/- 3.7e-01  |
 test_perturb_2                          |     -0.66 +/- 2.92     | -1.34e-01 +/- 5.91e-01 |  2.02e+01 +/- 4.7e-01  |  2.03e+01 +/- 3.6e-01  |
 test_proximal_jac_atf                   |     -0.42 +/- 0.95     | -2.96e-02 +/- 6.75e-02 |  7.06e+00 +/- 3.5e-02  |  7.09e+00 +/- 5.8e-02  |
 test_proximal_freeb_compute             |     +0.99 +/- 0.85     | +1.21e-03 +/- 1.03e-03 |  1.23e-01 +/- 7.2e-04  |  1.21e-01 +/- 7.4e-04  |
 test_proximal_freeb_jac                 |     -0.33 +/- 1.21     | -2.32e-02 +/- 8.41e-02 |  6.95e+00 +/- 4.4e-02  |  6.98e+00 +/- 7.2e-02  |