Fix some numba deprecation warnings

Trying to use `orcasong` CLI (in a Spack env on a Mac M1, for full disclosure...), I encountered the following warnings :

/Users/laurent/km3net/spack/opt/spack/darwin-ventura-m1/apple-clang-14.0.3/py-km3pipe-9.13.9-drhy2fp2hstkyii3gwlrue6iukqnkilc/lib/python3.10/site-packages/km3modules/k40.py:882: NumbaDeprecationWarning: The 'nopython' keyword argument was not supplied to the 'numba.jit' decorator. The implicit default value for this argument is currently False, but it will be changed to True in Numba 0.59.0. See https://numba.readthedocs.io/en/stable/reference/deprecation.html#deprecation-of-object-mode-fall-back-behaviour-when-using-jit for details. def add_to_twofold_matrix(times, tdcs, mat, tmax=10):

I know very little about Numba but following the doc linked above I ended up with this PR, which does seem to silence the warnings indeed.