Fix expired deprecation in scipy v1.14

[dnerini]

scipy.integrate.simps has been removed in favour of simpson, see https://docs.scipy.org/doc/scipy/release/1.14.0-notes.html#expired-deprecations

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.31%. Comparing base (8969e7b) to head (723b526).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
pysteps/verification/lifetime.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #455   +/-   ##
=======================================
  Coverage   84.31%   84.31%           
=======================================
  Files         160      160           
  Lines       13249    13249           
=======================================
  Hits        11171    11171           
  Misses       2078     2078           

Flag	Coverage Δ
unit_tests	84.31% <0.00%> (ø)

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