Replace legacy scipy interp1d in interp_time #916
Description
`scipy.interpolate.interp1d` is considered legacy since SciPy 1.12.
Remaining usage is in `DataArray.interp_time()` (`src/mikeio/dataset/_dataarray.py`). Replace with `make_interp_spline(k=1)` or equivalent.
The layered geometry usage was already replaced in #915.