Introduced task splitting in classical calculations

[micheles]

It quadruple the speed for the USA model 3% by solving the problem of slow tasks:

# master
| calc_6597, maxmem=146.5 GB | time_sec  | memory_mb | counts     |
|----------------------------+-----------+-----------+------------|
| total classical            | 95_404    | 393.4     | 385        |
| get_poes                   | 61_411    | 0.0       | 11_688_076 |
| computing mean_std         | 18_298    | 0.0       | 236_908    |
| ClassicalCalculator.run    | 2_178     | 1_606     | 1          |

| operation-duration | counts | mean   | stddev | min     | max    | slowfac |
|--------------------+--------+--------+--------+---------+--------+---------|
| classical          | 362    | 262.8  | 70%    | 25.9578 | 1_792  | 6.8164  |

# time_per_task=60s, concurrent_tasks=192
| calc_6600, maxmem=159.1 GB | time_sec  | memory_mb | counts    |
|----------------------------+-----------+-----------+-----------|
| total classical            | 42_038    | 85.2930   | 679       |
| get_poes                   | 38_681    | 0.0       | 6_731_012 |
| total hazclassical         | 18_455    | 146.7344  | 300       |
| computing mean_std         | 11_318    | 0.0       | 136_271   |
| ClassicalCalculator.run    | 551.2     | 3_892     | 1         |

| operation-duration | counts | mean    | stddev | min     | max      | slowfac |
|--------------------+--------+---------+--------+---------+----------+---------|
| classical          | 190    | 221.2   | 54%    | 25.2907 | 495.5    | 2.2405  |
| hazclassical       | 300    | 61.5173 | 27%    | 36.0467 | 114.1983 | 1.8564  |