fix: make scipy import lazy so mdfreader imports without scipy installed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ratal

mdfreader/mdfreader.py

@@ -38,7 +38,6 @@
 from numpy import arange, linspace, interp, all, diff, mean, vstack, float64, float32
 from numpy import nan, datetime64, array, searchsorted, clip, empty
 from numpy.ma import MaskedArray, masked, empty as ma_empty
-from scipy.interpolate import interp1d
 from .mdf3reader import Mdf3
 from .mdf4reader import Mdf4
 from .mdf import _open_mdf, dataField, descriptionField, unitField, masterField, masterTypeField, idField
@@ -766,6 +765,7 @@ def interpolate(new_x, x, y, interpolation_kind):
                 elif interpolation_kind == 'next':
                     return y[interp_close_point(x, new_x, 'right')]
                 elif y.dtype.kind not in ('U', 'S'):
+                    from scipy.interpolate import interp1d
                     f = interp1d(x, y, kind=interpolation_kind,
                                  fill_value="extrapolate")
                     return f(new_x)