[Breaking change] Include starting time (0) in `get_algorithm_time`

It seems useful if the entries of `get_algorithm_time` correspond to the ensembles in `get_u`/`get_g`. This would allow, for instance,
```julia
for (ensemble, t) in zip(get_u(ekp), get_algorithm_time(ekp))
# ...
end
```
Currently, the initial timepoint (`0`) is not included in `get_algorithm_time`, while the initial ensemble *is* in `get_u`.

Changing that might break people's code, however (including mine, now that I've worked around this).