Saving memory with multifault sources

[micheles]

Solves the CEA issue #11246. Here are the figures on cole:

| calc_99966435, maxmem=202.3 GB | time_sec | memory_mb | counts     |
|--------------------------------+----------+-----------+------------|
| total classical                | 467_253  | 1_060     | 720        |
| get_poes                       | 191_148  | 0.0       | 33_807_614 |
| computing mean_std             | 70_224   | 0.0       | 628_517    |
| iter_ruptures                  | 51_064   | 0.0       | 65_180     |
| nonplanar contexts             | 29_374   | 0.0       | 308_742    |
| building dparam                | 13_628   | 0.0       | 16_800     |
| planar contexts                | 6_716    | 0.0       | 2_005_008  |
| ClassicalCalculator.run        | 4_605    | 2_683     | 1          |

| operation-duration | counts | mean   | stddev | min    | max     | slowfac |
|--------------------+--------+--------+--------+--------+---------+---------|
| classical          | 568    | 822.5  | 26%    | 278.8  | 1_243   | 1.5117  |