Numba deprecation

[khider]

Is your feature request related to a problem? Please describe.
Numba is about to make changes to its API and we should check that it doesn't affect us.

The warning

/Users/deborahkhider/anaconda3/envs/paleodev/lib/python3.11/site-packages/climlab/convection/akmaev_adjustment.py:142: 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.

Describe the solution you'd like
We do need to have a look at the Numba acceleration as it doesn't seem to do much in terms of performance.