add 'sdpd' for slow simulations

[haakon-e]

Add printing of simulation-days-per-day (sdpd) for simulations where 'sypd' is very small.

For small `sypd`:

┌ Info: Progress
│   [...]
│   sypd = "0.002 (sdpd = 0.649)"
│   date_now = 2024-09-16T14:00:01.266
└   estimated_finish_date = 2024-09-16T14:00:01.312
solve!:: 1.549485 seconds (6.39 M allocations: 372.947 MiB, 12.32% compilation time)
[ Info: sypd: 0.002 (sdpd = 0.645)

For not small `sypd`:

┌ Info: Progress
│   [...]
│   sypd = "2.123"
│   date_now = 2024-09-16T14:00:01.266
└   estimated_finish_date = 2024-09-16T14:00:01.312
solve!:: 1.549485 seconds (6.39 M allocations: 372.947 MiB, 12.32% compilation time)
[ Info: sypd: 2.123